> I have found x1950 pro with 512 mem and dddr3,
> and x1950 xt with 256 mem and ddr2

XT has somewhat faster GPU than Pro. And for MorphOS at least, 256 MiB VRAM is the limit anyway, so that a 512 MiB VRAM card will show only 256 MiB. Memory type can be largely ignored I'd say.