In addition to height and weight, what is your skill level and what kind of riding are you doing?
I am 245, 6'3" and think my YZ250F has plenty of power for what I want to do with it. But I am a fairly slow and conservative MX rider and probably an average trail rider.
I think the low end power on the 250F is better than the 250 2 stroke and that makes things a little easier coming out of curves, but the 250 2s has much stronger power mid and up. I find that I have to shift and clutch bit more on the 250F, but the power is more predictable.
My biggest complaints about the 250F (in comparison to my Honda 2 strokes) are the engine braking, and the suspension (which I am obviously too heavy for), particularly the forks on the 2005. I like the power a LOT and I think once I get the suspension worked out, I am going to be real happy with it.