1) The 08+ models are MARGINALLY less powered than the previous models. At this level, nobody really cares about that. Gary Jaehne, 250 enthusiast and author of this site’s 250R review had this to say:
“It’s still only a seat-o-the-pants dyno impression at this point, but based on having run the new bike on the same combination of twisty backroads (including some with steep uphills) that I’ve sampled for the last 80K miles on my old-generation (2000) Ninja 250, I suspect that in stock emissions-legal trim, the ’08 model is putting out just a tad less peak HP.“
That’s peak HP, anyways, and what you’re missing in that statistic is that the fourth gen Ninjas (08+) have a much more balanced midrange, meaning there’s more power available to you in the RPM range you’d normally ride in.
2) On that note, the ’08 250R is a speedy vehicle. It supposedly gets to 60mph in 5.5 seconds with a good rider, and that’s a helluva lot faster than most cars. Plenty of sports cars can’t touch that. What you may not have figured out yet is that the 250 (past and present, but your past generation even more so) needs to be ridden in a higher rev range than larger bikes. All of the power is available high up. If you feel like it’s sluggish, but you’re not keeping revs above a minimum of 6-7K rpm at all times, you aren’t using the power delivery properly.
Back to the actual thread: I’m going to vote 650R though I think you’d be perfectly happy on a 250R. You’d probably be happier on the 650R.