If you didnt already have the 5D2, I'd say just get two pre-owned 5D, and mount your 50f1.4 on one, and a 28 f1.8 or 24 f1.4 on the other.
I hardly think that the older 5D can't produce what you need (based on your description of use).
On my part, I had a good copy of the 28 f1.8 on a 5D...