You can buy a set of 20cc domes to lower the compression. They are inexpensive and easy to change.
Myself I run 18cc domes and mix 100 octane and 93, done it for years and never had a problem. I run a 50/50 mix. I know anything close to a 50/50 mix is good enough to prevent detonation. That is all you need to do. And my banshee is not a garage queen it lives in the dunes and has been to trails all over the Midwest.
01' Raptor 720, Stage 2, FCR'd
97' 250 Vitos Blaster
06' Rhino 450
94' Banshee T-5's, Vforce, ported, Cool Head, 2-1
06' Wolverine 450 - Stock!
06' LTZ 440
94' Vmax4 750, 96' 600 MountainMax, 07' Nytro(b00sTed)
06' Vmax 1200