Nope, not talking about shutter speed. I'm talking about noise! Will images from a F2.8 lens on a 60D at ISO3200 be less noisy than a 5Dmkiii at 6400 at.
well, I think (don't quote me on this) that 5DIII outperforms 60D by more than a stop in terms of high-ISO noise.
If you prefer not to use f/2.8 (coz DOF may end up too thin) yet maintain shutter speed, then high ISO is probably your only solution