Graphics memory has very little to do with final image quality, since pre-rendered stills are still classed as "graphics" and even then with realtime graphics lots of other factors in the equation, not for the least what game it is and the engine, rez, display size, native rez of display? (ie LCD or Plasma) type of technology and settings, game settings like specialist video card options, draw distance etc. Motherboard type, FSB, graphics bus and bus speed, memory type, amount and speed. Drive revision,BIOS settings. You could have super hi def console but still using composite or RF to standard def TV! Connection type.
Fit two identical cards except for difference in memory, if both can keep up identical frame rates with same settings then both look the same right?