I've used the Planar T* 50mm f/1.4 (Contax/yashica) on the 5D and i just sold it because i'm changing my system. Maybe you can try, since it's much cheaper than the new version and probably as good.
The quality is wonderful and i found it much better than the Canon 50mm f/1.4 USM i used to have.
I already tried a lot of excellent 50mm primes, including:
Olympus OM 50mm f/1.4 (latest version)
Pentax Super Takumar 50mm f/1.4
Pentax Super Takumar 55mm f/1.8
Carl Zeiss Planar T* 50mm f/1.7
Carl Zeiss Planar T* 50mm f/2.0
Leica Summicron-R 50mm f/2.0 (E55)
Yashica ML 50mm f/1.4
Canon EF 50mm f/1.8
Canon EF 50mm f/1.4 USM
Nikon Ai 50mm f/1.4
The Planar T* 50mm f/1.4 was the one I kept, although most of the others were also amazing. Ok, the Canon f/1.8 produces an awful bokeh and the built quality is terrible, although it still very sharp.
The 50mm f/1.7 version is almost as good and cheaper, but it doesn't have the same aperture.
I also used the Planar T* 85mm f/1.4 (I still have it for sale on the forum) and it's also an amazing lens.