as use is determined by mostly what you have start off with and how it's programmed, and only a smaller % by drivers used, it may be better on some hardware configuration than others, i have tested it on 4 different pc set up, but with one common thing between them all, all intel cpu, and all amd graphics so can't comment on anything other than them, my finding are,
dual core, core duo E6850@ 3GHz with 6gb win 7 pro 64bit
dual core Core 2 Duo E8400 Wolfdale 3.0GHz 3gb of ram xpsp3 pro 32bit
i7 2700k cpu with 16gb of ram win8.1 64bit pro plus win 10 on dual boot
i7 3960X cpu with 32gb of ram win 8.1 64bit pro (4gb vga)
XP/WIN7/WIN8.1 and now win 10 BETA TESTER
there is little real difference between in game use to notice with the game at all, 2 have 2gb cards 1 has 3gb and 1 has 4gb....

- gpu use.jpg (240.18 KiB) Viewed 2518 times
2gb had 85% gpu max, with 3gb card and 4gb ones even less, and that was max use not all the time use, no spikes either, it spiked and went to 85% stayed there for a while then went down, never about in half an hour in took to finish the last mpa, and yes i've done it 3 or 4 times now.....
picked largest map and most amount of units in game and deployed and then move and ended turn, took this on enemies turn