Lenses do have a maximum f number they can be set to. This depends on the lens not camera. Most of the time it is not really important what this is, as you will enter a region of diffraction softening regardless of the lens.
In general, any lens set to f/11 will perform like any other lens set to f/11. However, be careful comparing fast lenses, with not so fast ones when close to their limit. For example, a 50mm f/1.8 lens used at f/2.8, will generally be "better" than a 50mm f/2.8 lens at f/2.8. In general, lenses get a bit sharper if you don't use them at their maximum but a bit below that.
_________________Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.