First, the KX250f is a great little bike, I had 250f's from 04-09, loved them that was my primary ride didn't get a 10 but did get a 11 (fuel injected)didn't like it, probably rode it 3 times got rid of it and got a 12 450. I weigh about 200 and it packed me around fine play riding but honestly I think it would have been underpowered to race. as for dependability, I never had issues but I take anal to a new level, pistons, valves and cam chains often, so are they worth it? only you can answer that question, they for sure cost more to keep on the trail, so, having said this, I would probably go for the conversion, it will clearly carry you and be much less expensive to maintain.