Realistically, I wouldn’t care less about Window’s Shells since with Windows it is all much of a muchness and you are using Windows at heart no matter different you try and make it look. I personally have skinned mine to look like OSX without the restrictive application at the bottom. It sticks out like a sore thumb and it is not nicely hidden away (in a convenient manner) like Windows does. Before you get hoity toity, I’m not a MS fan but you gotta pay it where credit’s due.

http://en.wikipedia.org/wiki/LiteStep
I wouldn’t think that while you’re changing the look that there would be any performance increase. To me, that would be the only thing going for it if it did increase performance. The look is quite boring. Even the grey-bar look aka Windows 98 default theme looks better than the box-look this LiteStep.