C12 is what I was running in my SV last year. It's meant for mostly for Twins and is 108 octane rating. It's more for high compression twins. MR12 is the best fuel this year, and it's damn hard to find. It will offer the most gain. Following that is MR9 and MRX01, both nothing to sneeze at.
For most bikes that are NOT built with engine work for racing, the most gain you will see is on U4.4 the new replacement for U4.2 this year. This gas will not rot your internals as fast as MR9,11,and 12 will do. If running race gas, always remember to drain your tank and the end of the race day and run a bit of pump gas through the bike to flush the pump empty of the race stuff. When it sits for a period of time, it will eat the coating on your tank, dry out your seals, and can corrode your fuel pump.
If you come out to Vancouver, Mspeed Performance has a lot of it for sale in 5 gallon mini-barrels.