Enudro, sorry I didn't see your question. But Rolex and others got it right. Am flying again because I've beaucoup time on my hands after a work injury. Same set up. IMac 24 with the optional nVida card they built into it.
Checking compatibility with Windows 95 in the HTC folder on the HTC black spade by right clicking on it solved all the problems. It's the same fix the guys use with the dual core AMD's. Or part of it if I said it wrong.
Frame rate stays steady at 60 even during massive mission takeoff. It does not go above 60 though. I've thought of looking for a whatever to allow for FR to increase, but have decided against it.
Works well enough for me.
For anyone tempted to go Apple, I'd say do it. The expense is the downside. Get one with the fast chip and good card.
You can save a good deal of money money by buying memory from another source than Apple. Mac Owners Support Group has a nice deal with some vendor. I got mine with 2 gigs (didn't know about the deal via MOSG) and have a opening to add a 3rd but haven't done so.