When estimating 1RMs I always think a safe bet is to halve the number of reps for every +10 pounds. This probably underestimates your 1RM a little but whatever, at least you don't sound like one of those douches who thinks he can d/l 500 lbs because he does 225 for 6.
Let's assume you could sack up and get 455x8. So 465x4, 475x2, 485x1. I'd say somewhere in the neighborhood of 500.