Moons ago we tested 20:1, 25:1, 30:1 and 40:1 on the dyno and track with a TZR250SP. It was a test for Castrol, using A747.
20:1 gave bad throttle response and power, and oiled the plugs at low rpm.
25:1 & 30:1 gave the same power, but 30:1 was crisper on the gas.
40:1 was crisp on the throttle, but scortched the bore at high rpm.
Jetting for every test was optimized.
I use 30:1 on the NSR. I use 40:1 on the CR500 Super retard cos it's a relatively low revver.