I ran 17.5 boosted to start with and if rollout is spot on,think I had mine at around 80mmpr it was plenty fast enough. I then went to 10.5 no boost and 10.5 boosted. I now run mod 5.5 and to be honest it's no a great deal quicker than 10.5 boosted on most tracks, but it's slot easier to drive in my opinion. And this is how the majority of racers at our club are also heading.
My advice would be to run higher turns till you get used to the handling the slowly creep up.
With respect to damage all I have broken in 1 year is a rear axal on my x11.