Mike McCann has made some great videos on suspension and performance mods for the TTR including the exhaust and front forks. See his YouTube channel here
His latest videos show the progress on a 350cc conversion using the Totally TTRs big-bore kit. First of the series is here:
As far as I'm concerned, it is not the top end power that is important, but the wide torque band that makes the engine so much more flexible. Mike has found it feels undergeared - getting into 6th much sooner and looking for 7th! From a travel bike point of view, it would allow higher gearing for better fuel economy and lower revs at cruise.
I found that an FMF end can made quite a difference to the pick-up of revs, even with the standard carb (rejetted) but made it too noisy for my trail riding preference. Can't remember if I did a dyno or not now. If I did it will be posted further down the 350 thread.