I'm fairly close to you strength-wise. (425 pound squat, 455 pound deadlift)
For what it's worth, I train Squat and Deadlift twice a week each, going for 4 or 5 sets of max triples usually. The first week of this much volume felt like I was going to die, I literally couldn't drive home after my second squat workout of week one.
After that first brutal week though, training both heavy every session seemed to really do wonders. Now, if I miss a deadlift day, I can actually feel it negatively effect my squatting, and vice versa. Anyways, the point is, at least in my experience, you can definitely push both lifts up at the same time, and I've found they compliment each other, very, very well.
I started this routine about six weeks ago, and I haven't not PR'ed in some way or another in any of my workouts thus far.