Will the 512mb be enough for gaming on native 1440x900 reolution gaming? Will the nvidia chip be able torun modern games on high-max? Should I go with the 6770m with 1 gb to be safe?
At that resolution it should be fine. Most modern games will run fine with that much of Vram, though i can't say with high end games like Skyrim, rage, etc. on windows
using an external screen up to 1080p though might have issues.