Your choice. And I do and quite confident taht there are no issues from server side with Vantage. I test it on multiple systems ATI/NV systems including 5770 and 5870 series but not on Crossfire (AMD cannot code drivers properly even for single GPU). And it is just pointless anyway, the server is regular DirectX application so there is ZERO dependence on hardware and zero hardware specific codepaths in it. It should work on any properly implemented DX driver, vendor or single/multi GPU config doesn't matter. There are explicit notes telling that the server doesn't native 64-bit applications in ALL tools using it (RT, Precision and Afterburner). There are dozens of threads with questions about it and answers in many forums including this one. And furthermore, there are direct question with my reply about 64-bit support roadmap submitted by Nick right on the first page of THIS thread. So start reading please and your issues will get addressed by yourself.