Re: 2 GTX 275s vs HD 5870
GTX 275 SLi = GTX 295. The HD 5870 trades blows with the 295 and it's cheaper, uses less power, only requires and single PCI-E slot, and you'll be without all the disadvantages of a multi-GPU setup.
+1 for the HD 5870.
AMD Phenom II X4 955 BE @ 4.0GHz + TU120E lapped - MSI 770-CD45 AM3 - 2x2GB OCZ DDR3 1333MHz - Sapphire HD 4870 - Samsung Spinpoint 500GB 7200RPM 16MB cache HDD - Tagan TG600-BZ Piperock - (Currently open test bed) - Windows Vista Home Premium 64bit.