I have an MSI HD 4870 1 GB and im looking to upgrade my rig to 2 graphics cards. but would 2 4870's in Crossire be the same performance as a single 4870x2? i mean im pretty sure the 2 in corssfire would have better cooling but like whats the difference?
Not, the performance isn't the same. Whe you have a crossfire, the cards divide the process between they BUT not add their memories. Whe you have a single card like the 4870x2, is an only card that have 2 cores for procesing BUT with a memory sure of 2GB in this case.
2 4870 1GBs in CF should be faster than a 4870x2 IF you have at least 2 PCIe2.0 8x lanes.
So go for the CF 4870s.
No they shouldn't...
The clock speeds are the same, the x2 has 8x per card, which is the same, the graphics cores are the same. In basically every way, the 4870x2 is identical to a pair of 4870s in CF on 8x slots. On 16x slots (for both cards), the pair of 4870s would have more bandwidth, but I'd be surprised if it made a significant difference.
Honestly, for all practical purposes, they are identical in performance.