How fast is fast?
I'll stick my neck out here. Had a KLR. Lots of fun but slow. The kid that bought it was coming off a smaller dirt bike and thought it was fast.
I now have an F800GS. Lots of fun. Faster than a KLR by far but still slow and heavy in the woods.
Stupid Fast = liter+ class bikes. Nothing like the grin created by highway wheelies and triple digit white knuckle holdin' on acceleration. My buddy has a '10 CBR1000RR. Another mutual buddy bought an '08 600 something and the CBR guy rode it home for him. He did not have the heart to tell him how underpowered his new to him bike was because he didn't want him to feel bad. Once you are bit with all that power it's hard to go slow again. For me it was Kid #1 that made me think hard about the triple digits. Kid #2 put me ATGATT.
Fun fast = most sport bikes (even out dated cheap ones will still make you smile) I rode a buddies SV650 that he gave $500 for and put another $1000 to fix up a bit. What a blast to ride. Yes I was smiling. Not my bike and not sure of the tires but I did scuff them in a bit and blew the carbon out.
Comfortable fast = most sport tourers and even big adventure and touring bikes. I miss the Aprilia RST1000 Futura on those long rides.
Any one bike for everything is a compromise. Street tires suck off road. Off road tires suck on road etc etc etc. I'm looking to add to the stable but more on the touring side. I'm thinking an older RT or maybe even a Goldwing. Did I just say that?? The Mrs. doesn't like the back of the GS so much. I do love her!!
The only cruiser I have ridden was a Harley V-rod. It was comfortable and lots of gusto (similar to the Aprilia Futura for power) but just not my thing.
I do cling to my Bible and Guns!