I have a 128mb Radeon 9800 pro, at 512 textures it was using approx 105mb of memory.
Using 1024 textures its now using approx 115mb of video memory.
It makes a difference how you have your card setup, personally i am using 4 AA and 8 AF and all settings in game at max and 1600 res.
In video driver setup again all settings at max quality.