I'm making a new computer specifically just to play civ 4 bts. Would getting a faster GPU be better than getting more video card memory? Or does it matter because the bottleneck is probably the main cpu? The computer is a AMD x2 4600+ winsor and I'm probably going to just settle for a 7300 gt w/256 mb, but i 'm also looking at the 7300 gt w/512 mb and 7600 gt w/256 mb.