I will be using it on a 5d Mark 2, i like what the 50mm does with the DoF on the FF body, will the 35L offer the same DoF Effects using a big apeture?
Which lens is going to be better, remember the DoF for me is of paramount importance.
DoF for the same framing is constant (with some exceptions, but this is not one of them). If you take a picture with a 35mm at f/1.4 and then move back so that the subject is the same size when using a 50mm, the DoF will be essentially the same at f/1.4 (neglecting differences in lens design). What changes is the perspective and how diffuse the background appears.
50mm at f/1.4 will have a more diffuse background (more subject isolation) than the 35mm at f/1.4. Using an even longer lens, even stopped down, will have even more background diffusion.
Choosing 35mm vs 50mm should really depend on what perspective you want. The FoV of a 35mm lens will make you move closer, which changes perspective, and you may or may not like that. If all you really care about is how diffuse the background is, then get the longer lens.
Like someone else said, you should consider the Sigma 50/1.4 over the 50L. All lenses made for Canon EOS mount that don't have EF-S, DX, Di II, or DC in the name will fit.
