Hello i bought a sapphire 4870x2 today and i got disappointed , . the reason is: when i had my 4870 i got avg 270 fps at high settings at Counter strike source , while i got avg 140 fps at high setting with my new sapphire 4870x2," both stresstest were at 800x600 ingame resolution".
my pc specs when i did both stresstest was as follow:
First of all, your power supply is two weak. A 550W is really the recommended supply for ONE 4870. Your card is probably not getting enough juice. Also, crossfire adds some processing overhead to your CPU so you mighnt wanna think about overclocking your chip. You also need more system RAM. I mean really you have more VRAM than system RAM!
Going from a 4870 to a 4870X2 isnt much of an "upgrade" when you factor in your PC specs and resolution. At that resolution even a 7900GT will give you like 200FPS in Counter Strike....you were already way...way....WAY on overkill as far as video card goes for CS with the 4870. Of course this is assuming CS is the only game you play. And has somebody already mentioned, anything over 60FPS is unnoticable and is preety much headroom for spikes and heavy graphical areas.
As far as teh rest of the system goes, I think hes ok with 550W but his PSU is an ASUS, so yea I wouldnt trust it. If it was a Corsair, PCP&C/OCZ, Mushkin, Antec or what not he would be fine with it. Also ditto on the above RAM comments, 2gb for XP, 4gb for Vista.
You won't see too many (or any) reviews with this card at 800x 600 but one pattern you may notice is top end cards under performing lower models at CPU bound resolutions. You may have no problem with your card but I agree with the gallery that the first set of specs you presented are very unbalanced and the PSU doesn't meet the requirements.