Crossers use those sort of mixes but they are rarely on full throttle for long - point and squirt. So if all your riding is in town then ok.
However, if you ring its neck on the open road and have the throttle pinned for a while then go 30:1 as a minimum. It will be a bit smokey in town but....
I have heard that for the Manx and TT people run 25:1 as the bikes are on throttle for so long.
Oil is cheaper than pistons, barrels and bodywork + your arse
