I purchased the same card from newegg.com(QUITE A DEAL)
I have paired it with my 5870.
Initially I had alot of issues with BF3. I have since worked them out. If you have any issues specifically with BF3 PM me.
As for it's performance? Awesome. I'm running an Eyefinity setup @ 5760x1080. I have all BF3 settings on Ultra, MSAAx8. I get between 50-80 FPS in BF3.