The biggest change to the bike besides cosmetics is the power. Its not really fair to compare a fresh big valve, 40mm carbed 1000cc engine to a 88K worn R80 engine with bad valves and low compression but that was the change. My son's first comment after his first short ride was "the thing actually responds to the throttle now".
To me the change in handling was as dramatic as the change in power. Again the comparison is not fair. The whole bike, especially the front end is way lighter. New wheel, swingarm, and steering head bearings, new tires, and an aftermarket fork brace all helped a lot I am sure. I love the riding position the new handlebars created. I worried that the riding position would be tough on an old guy like myself. I am 6' 2" (and shrinking) and find it very comfortable.
I often see people recommending changing the rear drive ratio when upping engine power because the stock R80 ratio is lower geared than necessary for the bigger engines. I thought for the roads I generally ride on keeping the stock R80 gearing would work great. So far I am very happy with it. It is turning the same RPM it did when it was 800cc. The 1000cc engine is supposed to vibrate more. I am not noticing that at all. Perhaps because this is a well tuned engine with balanced carbs. I never attempted to tune the R80 engine in the short time I ran it.
At 60mph the engine is turning 4000rpm. It feels smoother than the newer R100GS that was my last Airhead. The acceleration is brisk. We averaged 60-65mph on our trips. WE got 41-43 mpg which was much better than I expected with this gearing. I plan to keep it this way for now.