I'm not convinced any of the 3 models you mention would offer you appreciably better results than you currently get with your 500D. The 1D mk 2 is a pro body with more than double the fps of the 500D, but just over half the resolution (not quite so good for the large prints you say you do); there isn't really a significant enough difference between what you have and the 600D for me; and the only reason to go for a 5D is it's FF. Personally, i'd stick out for another 1Ds mk 2.
BUT...
I'm with KmH, it almost sounds like you're thinking that because you're using L series lenses somehow the 500D isn't good enough. The ONLY reason to upgrade bodies is if what you currently have isn't capable of delivering the results you want, not because you feel it may not be in the future, or because you haven't used it to it's maximum potential.