Well 1, 2 or 4 MD VRAM is really very out of date. I think most cards with eg. 4 MB are not supported by Direct3D. A lot of Games that are released today do require 256 MB or even more. I think it's ok to expect there are at least 64 MB if you plan to use DirectX 7 to its imits. If you really want to do something for retro hardware, you might think about to use a software renderer instead, that doesn't care about VRam.
Well in your calculation it seems you forgot there's doublebuffering, so you maybe need to double those numbers.
Well in your calculation it seems you forgot there's doublebuffering, so you maybe need to double those numbers.