a 250cc is actually the perfect size engine. It's the most versatile as far as aftermarket upgrades and easy to work on. I am 6'2" about 210lbs. and my yzf 250 with common aftermarket upgrades is more than enough power. A 450cc is a little larger in frame but the engine is too strong. I guess you would have to test ride a 450 just to get an idea of what works better for you. I recommend Yamaha.