I tend to work in half-plate and full-plate increments - they're easier to work with. Since I have found out that sumo tends to agree with me much more, I also tend to alternate between sumo on my warmups. For example I might do something along these lines the next time I go for a new 1RM:
135/3s+3c (minimal rest between the two)
405/1s (Still under 90% here, just)
455/1s (Previous 1RM)
And then go for a new 1RM. I 100% agree with you on the idea of limiting reps above 90% - hell, when I got my top set on deficits the other day, I could just *feel* the strength draining out of my arse and hamstrings. I figure I could have safely done another single or two at 95%, but I really wanted to get that 1RM on video. Oh, well.. the video attempt was a valiant effort.
Also, I believe that Dave Tate got the "No more than 4 reps at 90%+" from Louie Simmons, and Louie would say that once you've hit 4 reps at 90%+ you're done for the *day*. No assistance work, nothing else. Go home.