I lift at home and I also have odd shaped plates, only mine are actually worse (like stop signs). I'm actually thinking of buying a whole new set of rounded plates simply because of the problems doing deads with them.
Damn you're strong, but the rounded back would bother me. I really focus on keeping my back as straight as possible. I noticed you keep your head down a bit, I find that keeping my head up really helps to keep the back from rounding. The only tme I let it round is when I find myself losing concentration slightly, which is not hard to do on heavy deads. Of course, heavy to me would be a warmup for you...