Except for sand tracks, usually 250's have the fastest times, at least in the old daze when 500's weighed closer to 250 lbs, and 250's around 230.
Don't know about more horsepower equating lower lap times. Every track I've ever ridden, talking motocross only (easy 150 AMA races), 250's had more than enough power, and except for the 2 Sacramento sand tracks, 125's could have the lowest lap times....but can't beat the 500's.
Are you still in NewYork, like Unadilla?
I play about twice a week now, just bought a MicroRadOS racket to ease the shoulder problems of my Aero500's. Still play high level 4.0 doubles and top 3.5 singles...not running not good for singles.