850
In my opinion an 850, which is tuned accordingly.
If you get the right cam in, and flow the head, with some high comp pistons, as well as some bottom end treatment, it will be better.
That is my opinion, I am sure others will disagree.
My old 750 combat was tuned, with superblend mains, and that used to really rev and fly. It was probably faster than my current tuned 850. I don't think it was as strong though,
Jerry