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Wow...you got 17 SandyBridge systems...you are loadedHave an 17 sandybridge system and looking at a card for bf3
want to spend around 300/350 ish
looking at a MSI ATI Radeon HD 6970 Lightning 2048MB GDDR5
Theres the first issue, if there are any xfire issues
Secondly I personally prefer single card solutions to dual, having recently swapped form Xfired 4890s to a 560
And Finally, 2 6950s are overbudget