300 all the way. But, FWIW, I went from a 98 250 to a 99 300. Not sure what the diff is in my year 250 vs. yours. I'd guess my 250 is weaker than yours.
That said, I fell in love with the 300 within 10 minutes. It doesn't feel any less nimble in super-tight, tree banging stuff. It's actually a bit easier in that stuff, because the motor chugs so much better. It probably isn't any faster than my 250, just such a better (more torque) powerband. I rode it in 2nd & 3rd all day on my regular loop, whereas I'd be in shifting a lot more & using 1st a lot on my 250. On one big, power-robbing hill, I was in 2nd, and lost momentum. On my 250, I would have had to jam it into 1st, do a panic rev & pop the clutch, wheelie, lose control, etc. On the 300, I lost some momentum, shifted to 1st, grabbed a handful of throttle, and rocketed up the hill. Fast. No stab of the clutch needed, so no wheelie & loss of control.
I thought my 250 had good low-end putt-putt all day power. This 300 rocks. Plus, with an FMF TurbineCore exhaust, it sounds cool. ;)