Cedega the linux sorta version of cider that just gives the games a path to cedega without the publishers optimizing actually runs the game faster on linux that it dose on windows very often, now since cider is a direct descendent of cedega.It's iffy. Cider runs natively. It's very optimized; it ONLY includes the parts of Windows you need for the game, and nothing else. All the crap is stripped out, which might make performance better. But then there's the extra overhead of having it run on top of OS X.
They should be pretty darned close.
kwood, Cider is not virtualization.