Well, I go from a cruiser to a 650R, so it's not so difficult for me. They are two different styles so my mindset is different depending on which I mount. I don't expect one to be anything like the other....and they aren't.
Now, from the buell to the 650R, I'd say it's a comfort factor. the Buell is sporty and fun to ride for a bit, but the 650R is much easier to ride. And because it revs so much higher, it's not missing so much power. Your bikes are at a larger difference than mine though.
I'd suggest you upgrade the 500 for a 650R and you'll be just fine.
