I put 300,000 miles on an r80gs, lots of it 2 up. with that bike needing some TLC, I've been using an r100/7 and an r100r. usually 2 up also. I honestly can't tell much difference. the 1000cc motors have a little bit more grunt, but the 800 is smoother.
if it were me and the r80 is in good shape, I'd leave it alone and ride the wheels off it!