Fatboy or Fatbob?
I like the comfort of my dyna.
I would go the route of using Buell parts personally, you can get 100ish hp out of that engine.
Do yourself a favor and go do some test riding BEFORE you dump money in your little bike, I think you will find that the big ones just feel right.
jwb47 - if you beat Anorexia, I must've crushed it.

I love riding, I do enjoy performance, but me riding Harleys is my way of not looking like an utter dork (riding a scooter), but still being economic on fuel.. Besides I've always been a fan of Harleys. I won't buy a metric, so that wasn't an option.
I am completely satisfied that I bought a Harley-Davidson. My Sportster is a lot of fun, I recently went on a ride with a ducati 966, and a 1300cc Honda. I was the slowest bike of the pack, but only the ducati could handle better than me. It was a lot of fun to ride with others. I have made a lot of friends riding around, been hollered at several times to pull over and talk shop with other HD owners in their garage.
The Best of Harley-Davidson for Lifelong Riders



edit: Engine wise, that is. I'm mighty curious.