Radeon HD 4870 X2 and 4890 Crossfire?

I want to upgrade the graphics in my desktop (see system specs) and I've been seeing 4870 X2s on eBay from sellers with very good feedback for around $150-$200. Is it possible to Crossfire my 4890 with a 4870 X2? If not, I will probably still buy the card because dual-GPU and 2 GB of GDDR5 isn't exactly slow

Another issue is I'm not entirely sure if the cooling of my case is enough to do that safely or not... or even if my PSU could handle a triple-GPU setup.

I know the chips need to be the same for nvidia so I suspect it will be the same for ATI, so no, your out of luck.

Windows i7 920 said:

If not, I will probably still buy the card because dual-GPU and 2 GB of GDDR5 isn't exactly slow

It's still only 1Gb usable though.

1GB per GPU that is shared across the cards. Usable VRAM isn't accumulative. The 2GB is technically correct in that the card physically has 2GB - but mentioning only 1GB is usable is not good marketing)

4870x2 + 4890 = no worries.

Windows i7 920 said:

I want to upgrade the graphics in my desktop (see system specs) and I've been seeing 4870 X2s on eBay from sellers with very good feedback for around $150-$200. Is it possible to Crossfire my 4890 with a 4870 X2? If not, I will probably still buy the card because dual-GPU and 2 GB of GDDR5 isn't exactly slow

Another issue is I'm not entirely sure if the cooling of my case is enough to do that safely or not... or even if my PSU could handle a triple-GPU setup.

Take it from my experience (and I have a good enough idea of one seller you've seen) do NOT buy an X2 off of eBay. You'd be better off buying a 560Ti or something.