First, an adamantine golem's slam attack deals 6d10 damage, not 30d10.
If I were to advance the golem's attack by one category, I would increase it to 8d10. The reason is that other attacks dealing 6 damage dice increase to 8 damage dice (6d6 and 6d8 increase to 8d6/8d8 respectively), so it would make sense for an attack dealing 6d10 to also increase to 8 damage dice.
You're right its rediculous. If it has to be done, then yes it looks right to me. Practically speaking though, if I were to use it in combat I would figure out a way to speed it up. Maybe 6d8 X 10. I must add though that I can't think of any reason a creature would need to inflict that much damage. Even if a character had 10 hp per level, that would only put him at 200 at 20th level, and the average of 60d8 is 270.
Then again, Are's response makes alot of sense.
Actually, what happens is that every two steps damage doubles, with a couple kinks.
d3, d4, d6, d8, 2-12, 3-18, 4-24, 6-36, 8-48, 12-72.
d10, 2-16, 3-24, 4-32. They specifically note in the weapon size table that 2d10 converts to a size larger as 4-32, so the next step is 6-48.
So, 6d10 will convert to 4-32 x3, or 12-96 damage, if a size larger.
PERSONALLY, I'd kick it up to 8d10, and the next step would be 12d10.
Yes, with Greater Vital Strike, this would really, really hurt.
==Aelryinth