They will be just fine with an 80 x-over. I've played them at reference with a 60hz x-over a few times on pink noise, etc to see what kind of distortion or excursion I'd get and I found that 80hz sounded a little less strained to me. 100hz is fine too, but it's going to be that much easier to localize a sub or subs and you're getting rather high in the passband unless you have a sub that can play up that high very cleanly.
By the way, I hate how AVR's only give you 60,80,100. I want increments of 5! Thought about picking up a mini-dsp a few days ago, but I just don't have time to do everything with it.
Panny 65st60 / Denon X1000 / EMP e55ti / EMP e56ci / EMP e5bi / (2) e1010i