i would say take the 5d mk2 over the 1d mk3 for the following reasons
smaller form factor
Full frame benefits
if you crop the 5d mk2 image to 1.3 crop you get 10mp anyway so same res as the 1dmk3
about a stop better high iso
the only thing better in the 1dmk3 is weather sealing and good AF (assuming you get a late model that didnt have AF problems)
..and more than twice the framerate, plus all the good stuff to customize. Can't remember if the mkIII had it, but one function I can't live without in the mk4 is the ability to set upper and lower limit of shutterspeed. The only way to shoot concerts.
1dx, 35 L II, 85 f1.8, 200 f2.0 L (yes, it's back!), Profoto B1