There's a 20 year gap in my model flying but that is the first time I've ever heard of anyone having too many RPM with an engine . . . ever.

That's why it's called a throttle and they don't just use an on/off switch. ;-)

If you're beating 17 grand with an 11 x 6 I'd say the 11 x 7 is a good next step. That will make you faster but less torquie all else being equal vs. the 11 x 6 choice.

Personally, I'd lower the top end with a end-point adjustment from the servo. Cheaper.