I started riding May 2010, and by mid June I was complaining about my bike…mostly that I didn’t fit the bike, but also that I craved more power…now that I have been riding another few weeks, I have figured out that my bike is powerful enough to have lots of fun and keep up with traffic…and as for the fit, it will come with time…your body will get used to what ever you decide to ride. If you are looking at a Ninja 250, your knees will be bent more than if you are looking at a Honda Rebel 250, or an enduro (dual sport) type of bike like a Suzuki DR200…all of them will move you along pretty good, and you will think they are quite fast for the first few rides. They can all get up to hiway speeds, but after a few weeks (depends on how much you ride it) you will get used to the accelleration, and want more…you just have to realize that your first bike is for learning, and not for being the fastest or coolest set of wheels ever. With you being taller, you will probably find the enduro bikes more comfortable, but that doesn’t mean that you won’t get used to the Ninja…it will just take a little getting used to. I find that stretching and getting more limber before rides helps (although I’m certain that you are in better physical condition than I am), and once you are comfortable on the bike, go for longer, and longer rides to get your body used to the riding position.
Just remember that when you are picking your first bike, lighter and comfort will be more important than fast and cool…the other bonus of the smaller bikes…fuel economy…you will get 60+ mpg out of the 200-250cc bikes, not that bigger bikes are terrible…but it sure is nice to get out of a truck that gets 16mpg, costing me about $125 per week in fuel, and getting on a bike that only costs me about $30 for the same distance travelled…and it is much more fun on the bike.