I just did 1500mi in 3 days on my XB12R (Firebolt) a couple of weeks ago. Here's some impressions/thoughts:
-The stock seat is HARD and THIN. It didn't bother me too much for the first 800-1000mi (day and 1/2) but it rapidly went down hill from there. My butt and upper thighs were SORE when I made it home! I think some padded bicycle shorts under my jeans really would have helped as my thighs felt "rubbed raw" from the heat/sweat/pants. They are on the "to buy" list before my next trip. Corbin still makes a seat for the Bolt. It's a little pricey at $250 but may very well be worth every cent if it makes long distance riding more pleasant. I've very seriously considered saving for one.
-If you're long legged you can get a set of lightning pegs which are 1" lower than the std. Firebolt pegs. They make for a pretty roomy ride and were EASILY worth the $40 I paid for them. I found mine on E-Bay brand new from Grand Rapids Harley (GRHarley). They are still readily available from a variety of places.
-Stock bars on a Firebolt are a little low and forward but really no worse than your ZX10 and certainly better than the Duc. There doesn't seem to be helibars or anything available for the Firebolt so if you can't live with the "leaned forward" position for long rides a Lightning may be a better choice.
-The little fairing on the Firebolt does actually provide
some wind protection and is nice on the highway and on colder mornings. There are a couple of windshields available too that may provide even more wind protection.
-Vibration is not an issue until you get up around 80mph. 65-75 is the "butter zone" and the bike is VERY smooth at those speeds. If you avoid the interstates (the BEST riding is on the 2-lanes anyway) the vibes will never be a problem.
-The ride is firm and the wheelbase is short but I never felt "beat up inside" from a days worth of riding, except for my butt.
The beauty of an adjustable suspension is that you can soften it up a bit if that is a priority to you. I have mine set to a pretty aggressive setup and it still didn't bother me for the 1500mi I did.
-One thing you'll LOVE about the Buell though is the gas mileage. I averaged between 55-64mpg over my entire trip; the 55 being my worst and that was the tank that included riding the Dragon. Even with the small fuel tank 150-175mi is possible.
-As far as how long before a good break;I can do 400-500mi days w/o too much of a problem on a stock Bolt but 3 of them consecutively seemed to be a bit much. I typically stop for a stretch every 2-2.5hrs (120-ish miles) and I can go all day like that. By the end of the day I am tired and ready for a GOOD break but just 15min stops for gas, a drink, and a stretch/walk is plenty.
Basically, if you can ride all day on a Japanese sportbike you will probably find the Bolt to be a pretty comfortable place to be. The riding position is agreeable, the torque makes for a nice relaxed ride (you SELDOM
need to run more than 3000rpm) and the overall bike is pretty comfy, save for the seat.
Hope my LOOONNG ramblings help.