This was already done, the general consensus was 400-700k, and I agree with it seeing it around the 600k range.
When it was announced dudes laughed @ me when I said it would do over 300k's. (I think it's safe to stick to that right)
I could see it doing a little better than general consensus of about 500k, but I can't see it doing a million. 500k would be a very good number for these guys.
given the magnitude of the fight, the way its being promoted by hbo and that its on september 15th ill say close to 1 million