I've been using that Golem lead a lot and I actually really like it. Sucker Punch is definitely the way to go, as it stops him from having to choose between setting up Stealth Rock and damaging the opponent's team. It's also the only other thing that sets him apart from Rhyperior. Here's how it's been faring against common leads:
Froslass: Rock Blast breaks the sash and KO's unless you get unlucky. Sucker Punch isn't advised since many just spam Spikes till they die.
Uxie: Fairly poor matchup, since Rock Blast and Sucker Punch don't hurt it too much. I usually just explode, which kills Scarf variants and severely maims defensive ones. If you have Pursuit you can guarantee Uxie's death. The best situation is when it Tricks it's Scarf onto you, then you Explode, then Pursuit it afterwards.
Ambipom: If it's smart, it will break your sash and run, so you'll have some prediction wars trying to damage its team. If it Low Kicks, you can 2HKO with a combination of Earthquake and Sucker Punch. During my testing, they always tried to Taunt or Low Kick. Golem's seemingly obvious Stealth Rock helps a lot here.
Moltres: Again it can unfortunately break your Sash and run, but if it attacks it dies.
Alakazam: Rock Blast stops all variants, but Sucker Punch can leave you Sashed if it's a Trick Specs that decides to attack. You also have a chance to remain Sashed if it's a Sash variant that uses Taunt.
Electrode: Rain Dance then Earthquake. Golem is nearly guarantee'd to get another KO unless you do something really dumb like Explode on a Rotom (or if it's Flare Blitz' weird Sash Kabutops >:O).
Omastar: You outspeed and 2HKO. Either it's no Stealth Rock for them or they have to face a Sashed Golem with Explosion.
Hippopotas: You can't 2HKO defensive variants, and Exploding on a Hipipopotas seems wrong, especially with risk of Focus Sash. If you know it's Leftovers you can explode to deprive them of Stealth Rock or you can switch and hope your spinning is up to snuff. Not a great matchup. At least Sandstorm teams are full of things that Golem can outspeed and hit Super Effectively / Explode on.
Rhyperior: You outspeed and 2HKO. Just like Omastar in the sense that they can let you keep your sash or they can get SR up.
Cloyster: You outspeed and KO with Explosion like 2/3 of the time. Chances are they've lost their Spiker / Spinner.
Arcanine: I never came across any that used Will-O-Wisp, so I always Exploded for the OHKO (even at -1).
Venusaur: If you don't have a Sleep absorber or cleric, it's going to be a case of "Golem is asleep and useless for the match" when you come up against Venasaur (the Sleeping Golem does sometimes make miraculous late-game Sucker Punches!). It never used Leaf Storm on me when I was testing this. If you have Chansey or Altaria then you'll be fine, just bring Golem back in before they set up Stealth Rock.
Hariyama: Outspeed and KO with Explosion, though it's prudent to use Earthquake the first turn just in case they lead with Protect.
Kabutops: Its Sash and Priority beat out yours. Most likely you end up with a 1 HP Golem and Stealth Rock on your side. I actually killed a lot of Claydol, Torterra, and Mismagius in this phase, which is just funny. If you have spin support this isn't the worst outcome.
Snover: Outspeed and KO with Rock Blast. Ice Shard doesn't do that much, and Golem is losing his Sash to hail anyway.
One thing that's cool about this is that it's really good at killing setup leads, who are really nice to have out of the way when you have spin support. It also outspeeds and 2HKOs Nidoqueen, Regirock(only 1/3 chance) and Steelix (2/3 chance) with Earthquake, while it outspeeds and OHKOs Donphan with Explosion. It wasn't unusual to get 2 KO's with this, and it was rare not to get any. All in all I think it worked out as a decent offensive lead.
Froslass: Rock Blast breaks the sash and KO's unless you get unlucky. Sucker Punch isn't advised since many just spam Spikes till they die.
Uxie: Fairly poor matchup, since Rock Blast and Sucker Punch don't hurt it too much. I usually just explode, which kills Scarf variants and severely maims defensive ones. If you have Pursuit you can guarantee Uxie's death. The best situation is when it Tricks it's Scarf onto you, then you Explode, then Pursuit it afterwards.
Ambipom: If it's smart, it will break your sash and run, so you'll have some prediction wars trying to damage its team. If it Low Kicks, you can 2HKO with a combination of Earthquake and Sucker Punch. During my testing, they always tried to Taunt or Low Kick. Golem's seemingly obvious Stealth Rock helps a lot here.
Moltres: Again it can unfortunately break your Sash and run, but if it attacks it dies.
Alakazam: Rock Blast stops all variants, but Sucker Punch can leave you Sashed if it's a Trick Specs that decides to attack. You also have a chance to remain Sashed if it's a Sash variant that uses Taunt.
Electrode: Rain Dance then Earthquake. Golem is nearly guarantee'd to get another KO unless you do something really dumb like Explode on a Rotom (or if it's Flare Blitz' weird Sash Kabutops >:O).
Omastar: You outspeed and 2HKO. Either it's no Stealth Rock for them or they have to face a Sashed Golem with Explosion.
Hippopotas: You can't 2HKO defensive variants, and Exploding on a Hipipopotas seems wrong, especially with risk of Focus Sash. If you know it's Leftovers you can explode to deprive them of Stealth Rock or you can switch and hope your spinning is up to snuff. Not a great matchup. At least Sandstorm teams are full of things that Golem can outspeed and hit Super Effectively / Explode on.
Rhyperior: You outspeed and 2HKO. Just like Omastar in the sense that they can let you keep your sash or they can get SR up.
Cloyster: You outspeed and KO with Explosion like 2/3 of the time. Chances are they've lost their Spiker / Spinner.
Arcanine: I never came across any that used Will-O-Wisp, so I always Exploded for the OHKO (even at -1).
Venusaur: If you don't have a Sleep absorber or cleric, it's going to be a case of "Golem is asleep and useless for the match" when you come up against Venasaur (the Sleeping Golem does sometimes make miraculous late-game Sucker Punches!). It never used Leaf Storm on me when I was testing this. If you have Chansey or Altaria then you'll be fine, just bring Golem back in before they set up Stealth Rock.
Hariyama: Outspeed and KO with Explosion, though it's prudent to use Earthquake the first turn just in case they lead with Protect.
Kabutops: Its Sash and Priority beat out yours. Most likely you end up with a 1 HP Golem and Stealth Rock on your side. I actually killed a lot of Claydol, Torterra, and Mismagius in this phase, which is just funny. If you have spin support this isn't the worst outcome.
Snover: Outspeed and KO with Rock Blast. Ice Shard doesn't do that much, and Golem is losing his Sash to hail anyway.
One thing that's cool about this is that it's really good at killing setup leads, who are really nice to have out of the way when you have spin support. It also outspeeds and 2HKOs Nidoqueen, Regirock(only 1/3 chance) and Steelix (2/3 chance) with Earthquake, while it outspeeds and OHKOs Donphan with Explosion. It wasn't unusual to get 2 KO's with this, and it was rare not to get any. All in all I think it worked out as a decent offensive lead.