like they said, the 1500 is likely to be bloated, fat, and ill-handling compared to your nimble speedy. It will be powerful comparitively, but if you like the speedy the 904 could be a good option.
I just installed a 904 kit in my bonnie a few months back and it has changed it into a fire breathing monster! I'm going to get some mikunis next, I can't imagine the 1500 being as nimble as our "little" bikes. Think long distance cruiser w/ low down power more than a nimble sporty bike.
btw, check out this vid of my 904:
http://s79.photobucket.com/albums/j158/sweatmachine/?action=view¤t=sweat904august07003.flv