the 7950 is a better value. the 7950 is a tahiti chip with 1792 shaders 32 ROPs 112 TMUs with 3gb VRam with a 384 bus width
the 270X is a picairn chip(7800 series) with 1280 shaders, 32 ROPs 82 TMUs with 2gb Vram on a 256 bus width the 270X is essentially a rehashed HD 7870 GHz edition with slight clock changes and a new reference cooler.\
by simple logic, 7950>7870 therefore 7950>270X