I don't know the top speed - I can guarantee it's nowhere near what my KX125 is though.... but it's not supposed to be. I bought it to be a trail bike and it has never left me wanting more -- I'm mostly riding in the woods, and usually do not get above 3rd gear.
I bought mine from
www.motofanatix.com and at the time it was $1000 shipped... it doesn't look like they still offer the DB-2 (which is what I have - with the inverted forks) -- but I think there's another Hensim dealer on here that may be able to help you find one.
I'm very pleased with this bike. I had it out last weekend for almost 5 hours of riding through tight woods, deep creeks (had the airbox under a couple of times for brief periods -- was a little scary, but luckily it kept on plugging along), large rocks, long hills.... it was a good ride.
My chain did stretch again - it seems like if I ride more than 3 hours it will pop off after a hard hit... this time it happen to be in the middle of a creek. :roll: -- fortunately the water was only a little above my swingarm so I just popped the chain back on and it was fine for the rest of the day.
Tom, If you are looking for top speed type of riding then you probably want something other than one of these 150's. They are nice trail bikes, with good manageable power, but they are not top speed monsters.