Have you heard of 512x512 hi-quality head textures Ez? 512x512 of this head may look epic ingame.
What im basically saying is that you don't see very much difference ingame unless you zoom in, so the 512 size is basically useless. 256 is more than fine.
Tweakin: Its pretty good, but Membrain have made a very good version of this head, even though it needs some fixes.