Having owned a lot of boosted cars, they may claim that they offer better mileage, but in truth boost is so addictive you'll be playing with the throttle all the time and drinking the gas.
Oh yeah and on the bike end of things, I owned a Yamaha FZ6 and an R1, and after selling them I borrowed a friends brand new Ninja 250 for a group ride. That thing was a blast! However, I'd feel more comfortable on something a little bigger. Maybe a used Ninja 500 or something. My FZ6 ran a 12.0 second flat 1/4 mile with me driving, and got great mileage.
If I were buying a bike again today, I'd think long and hard about an FZ8 Fazer8 or whatever they're calling it.