The 80mm will have more torque provided that your ESC and batts are capable of putting out enough amperage. It would be interesting to put my 70mm (2000KV) motor in my Muggy with the same pinion and see what kind of difference there would be. I ran a 24T pinion at first just to see how insane it could get but I'm running a more conservative 16T now. If I can get a cameraman I'll try to get some video of it, it powerslides very nicely and busts through several inches of snow. As long as I don't high-center it on the snow it can blow through.
EDIT: Did you do anything to the Center Diff? The first thing I did after stripping the nitro crap off when I bought mine was pull the CD and put 30K fluid in it. I can still wheelie and it balloons the front wheels as it does it but it really helps to make it 4wd instead of FWD
If you get the 80mm you'll probably also want to oil up the front diff, I can unload mine pretty easily and will probably get some 10K for it to hook up through on-power cornering.