I've posted on this one before. Here is a different way to think on it. Stiemsma is a year younger than Perk. He has room to improve as it is only his rookie year. I actually think he could be a starter right now for a handful of nba teams.
Perk is a starter who plays limited minutes for possibly the best team in nba. Perk is not going to improve his game from where he is now. I'd love to say he will start averaging 10 rebounds a game (which he should) but it isn't going to happen. So Perks peak was with us prior to injury.
Now if you are the captain for a pickup ball game who would you pick. Greg at his current level, CURRENT. Or Perk at his peak. To me its stiemsma . Perk at his peak would play good low post positional defense, block shots well, he'd rebound and set picks ok..no better. His offensive game was horrible , couldn't pass at the top of key, couldn't shoot at free throw level or further. His interior offensive game was bad, he couldn't shoot free throws.
Greg can play good low post defense (not in perks class), call him an equal shot blocker to be nice to perk, rebounds better or boxes out, sets picks about equal. Can hit the outside shot, an average passer,can also run the floor much better, hasn't shown an interior offensive game except pick and rolls, can shoot free throws.
I honestly don't think they compare at perks peak. Greg is going to get better (resign him!) while Perk has leveled out and okc is going to be looking hard at that contract for the rest of it.