I've only put about 500 miles on it since the change, but so far, so good.
Only real improvement I've noticed is absolutely NO valve clatter. With the Mobil 1 0w-40 I would experience frequent valve clatter, usually just for a few moments after startup. Amsoil is spendy, but not that much more than Mobil 1.

The variances in motor oil are much more noticeable on bikes because (as I'm sure you know - just pointing it out for the unfamiliar) most bikes have a wet clutch and the type/viscosity of the oil will have a very noticeable effect on shifting.

Another note: I bought my ZRX used with 9,000 miles on it. Ran Amsoil in it since I bought it. Tore down the top end to do a overbore with hi-comp pistons, cams, etc. I ride that bike HARD, and the internals of that motor looked NEW, and slick as hell. I'll never use anything else.