I just got 455x2 this week. I can't wait to get back in and work up to 5 plates. The only thing is once you hit 5, you know you'll want to get 6. Ah deadlifts, how you own me.
although I havent quite hit 600 on either lift, I will say that the road from 500 to 600 in both the squat and the deadlift go way faster than 400 to 500. I think 5 plates on the bar is a mental barrier and once you get over the way it "looks" you just move one - old news