To add some real world experience to this thread:
I have an EVGA GTX 285 for Mac in an early 2009 Mac Pro. It's in slot 1 (the bottom slot). I have a RocketRAID 4320 in slot 2, and the GT 120 it came with in slot 3 (so that PhysX can use it as a secondary GPU). Slot 4 is empty.
When playing _any_ 3D game in Windows, this card overheats and locks up the system. The only way that I can play anything is to use EVGA Precision to set the fan speed at 90%. Then I can play Crysis without any problems, with excellent frame rates.
On the Mac side, if I'm doing lots of filesystem activity on the RAID, the GTX 285 can overheat and lockup the machine. This even happens when the 285 is doing nothing at all, just sitting at non-moving desktop. I imagine it's because the RAID gets hot enough (it has its own fan too) that the 285 just can't hack it.
My 285 seems to artifact and/or freeze at around 84C. I'm going to call EVGA tomorrow, as this is pretty unacceptable. It's OK on the Windows side because I don't use RAID much and I can increase the fan speed; but on the Mac side I have no option to increase the fan.
I have the AC running and the house is fairly cool. I even have a small task fan sitting near the back of the machine, trying to evacuate all the hot air coming out of the back of the Mac Pro.
The Mac Pro itself says the ambient temp is 31C and its running the Expansion Slots exhaust fan at around 1200rpm right now (the fastest fan in the whole box).
I think it might be because your case fans are not ramped??? Not sure, but worth investigating. I don't have crysis, but in 3DMark Vantage with my GPU fan at 65% I hit a max temp of 75c. Here's a post I made in another thread about the case fans. It's what I use while also bumping my GPU fan to 65%. Hope it helps...
Anyway, here's my 2 cents on this... When running 3DMark Vantage in Windows my CPU hits a max temp of 76c for a second or two but it never goes over with my current fan setting. I would prefer it stay under 75c but it's not possible if I want to keep my MP as silent as I like it in Vista... I find in OSX it's a different story, I never push my MP over 65c (ever) since OSX seems to measure the heatsink temp and not the core temp. This is why I don't really believe what I see using istat in OSX. I would hate to be close to "TJ Max" and not know about it.
To control my fans in windows (bootcamp not virtual) I first boot into OSX, switch profiles with smcFanControl and then reboot into vista using bootchamp (broken in SL). The reason is because the 2009 MP fans do NOT ramp up in vista. It's pretty much a sure fire way to fry your computer, since this is Apple's undocumented "feature" of bootcamp. I don't know if the new bootcamp in snow kitty solves this, but I don't really think it's fixed knowing Apple.
Anyhoo, these are my fan speeds in Vista:
Cooling Fans
Fan #1 1239 RPM
Fan #2 887 RPM
Fan #3 1217 RPM
Fan #4 1217 RPM
Fan #5 1817 RPM
OSX equivalent: #5 is BOOSTA, #3 & #4 Intake/Exhaust, #2 PS, #1 PCI
To control my fans in OSX I use this below. It's a awesome little application that Concorde Rules modded from an old program. Works like a charm in OSX on a 2009 MP. IMO, it's a billion times better than smcFanControl because fans are adjusted dynamically. You don't have to switch between profiles (like you have to with smcFanControl) the fans will go up and down as needed. Plus you won't be abusing your fans by leaving them ramped up as a constant in OSX.
https://forums.macrumors.com/threads/738163/
Please thank this guy for this, to me he's not getting the credit he deserves!