Go for it. Get the 10 if it's what you want. I'm too big for a 250 so won't tell you yes or no. I'll always take a 450 over a 250.
I have an 11 and noticed a different feel to the bike when it was new. Like any new bike it always feels weird but I maintain the mindset that I need to adapt to it. Certain items will always be modified to better suit my height and weight but attempting to re-engineer a bike or fight it's genetics is pointless. Over 20 years of riding and a dozen or so bikes I've NEVER felt "comfortable" on any in the first 10 hours of use. After 50 hours it is one of my favorite bikes. I ride offroad, and the YZ cuts up single track like no other and being a MX bike handles jumps and whoops better than any offroad bike will. The light front end is such a benefit when lifting it over obstacles, however it has never been an issue with hillclimbs or under hard acceleration.
power tuner is the best money I've ever spent on go fast parts. The tunability of the engine is mind blowing. No single bolt on part could ever offer the performance options of the Tuner. Ride a bike with a mud map
and then reprogram with the Marmont map
and you'll swear you just swapped heads, cams, piston, exhaust
and jets in five minutes.