Changing the restrictor on the LRP wont change the power by a great deal.
I tried it while experimenting trying to get some run time out of the sucker for the mains.
If you run spektrum then just go into you EPA's or travel feature and turn the throttle down to, say 60% as mentioned above.
I was, and sometimes still do, run the Spec3 in my RC8T and there is no .21 that will keep up with it on race day.
There is a Hara Series Vspec that isn't too far behind but no cigar.
The only motor that will outpower the LRP is the GRP tuned .28, but because of their bearing failure problems and initial price you picked the right mill!