Hey guys, So my 3870 X2 finally arrived today. Good news and bad news. In Vista/XP, both the 3870 X2 and 2600 work together fine, no loud fan issues or anything (the 3870 X2 is actually almost as quiet as the 2600 when idle, gets a little loud under load though). I have the 2600 in slot 3, and the 3870 X2 in slot 1. The system sees them both and has no issues, as they use the same driver suite. Unfortunately, in OSX, the 3870 X2 has it fans go near full blast constantly (it's not as loud as the 2600 full blast, but it's annoying). So if you constantly switch back and forth between OSX and Windows, this card may not be for you and you should just get the 8800. If you switch back every few days, you only need to set aside 5 mins to unhook/hook the 3870 X2 each time. I think that's a small price to pay to be at the top of PC gaming. The 3870 X2 works very well coupled with the mac pro. In most quad core gaming PCs with the X2, people can only load Crysis at resolution 1280 x 1024, All High, and No AA at around 30 fps. I'm happy to report that with the Mac Pro, I am able to run it at DX10, 1440 x 900, All Very High, and 4x AA, and get those same 30+ fps easily (I'll post youtube videos later). I don't care about using the X2 in OSX, but I do wonder if OSX having the 3870 kexts could at least solve the fan problem, as the X2 is two 3870's slapped together... I'll leave it to the hacking gods.