If you're running full range towers, You'll definitely hear a diffeerence when moving up to either the 4800 or 5800. I like the processing of the 3801, but there is a discernable difference just on power alone. In fact, I'm very impressed with the Denon 4800's sound, which, in my ears, proved better than Yamaha's RXV-1 (not as smooth, but the power definitely made it the more comprehensive receiver).
If you plan to add an outboard amp the 3802 + a solid 2-3 channel should yeild excellent results as well.
Elbert