They are both 128-bit, 256MB RAM is enough for card of this category. 8600 and 9600 (both mobile) are nearly the same chips, but the manufacturing process on the 9600M almost eliminated the 8xxxM problems, so go for it (also unibody casing is much better). The 9600M also has higher GPU frequency, so is the power is same as the desktop 8600GT, which is slow for gaming, but enough to run all games at least on low settings, they are nearly the same, but i prefer 9600M... it will work longer than month. 256MB VRAM isnt a big deal for this card. I had 8600GT 256MB for desktop PC about 3 years ago and it was ok for 1024x768 - 1440x900 gaming, some games wont let you choose textures higher than medium, because of the smaller VRAM, but it shouldnt have any performance impact. 512MB VRAM will be better for higher textures, some texture packs and mods (like those for HL2, Oblivion or Fallout 3) It wont be faster. Still all games on the market should be playable.