1. Are you happy with the 48? If so then do you really need to move to a larger bike? Is it for longer tour trips or bar hopping?
2. The larger bikes would be a bitch to try to back up an incline and the risk of dropping at some point would be high. Can you ride up the incline and then back down as that would solve the problem.
3. All the big twins feel top heavy as they weigh a truckload more than a sporty (I have one of each so can attest to this). they may 'feel' more solid on the road due to weight, but I find they are slower to throw around and cannot stop anywhere near as well as a Sporty.
Have you considered a 1200 kit? they will turn a mild Sporty into a scalded cat!
Interesting thread... I have an 09 883 Low and I'm 6'2" so cannot comment on the height thing but find it a very comfortable bike to ride. Be careful with slimmer seats as they tend to strip out the foam and it then becomes a bloody sore ride (use gel inserts would be my idea).
Pop onto the Harley site as they list all the seat heights for the various models so you could then target a bike to suit. plus you can normally drop the rear an inch or two with lower springs etc