From my stand point a quart of Amsoil costs 8.05 a quart Mobil one 5.70 the price difference is insignificant at 2.35 per oil change, If I'm lucky I change the oil 20 times a year thats 50.87 a year including taxes 7,000 bike, 1,500 to do the motor 100 do do a clutch, it's cheap insurance to use a good oil.
if everybody whants to keep it safe, change the oil more oftenly, the issue is not that it degradates, it is that it gets dirty. whe have to keep it cleen.
why YAMAHA´s changing interval on previous 400/426 models was ONE race? the oil din´t take it 2 HOURS? NO. it got dirty from that net type filter letting everything but the biger shavings go thru whatever the oil it would use.
now the 06 YZ450 has a paper type filter leting the oil stay clean for 5 races/10 hours but still the oil comes as much dirty like on the previous model.
on those intervals the semi-synt takes it as whell as a full synt, com´on... it´s only 8 or 10 hours it has to last.
you guys are lucky that you don´t let go 20$/plus each quarter for a synt mobil, shell or repsol like whe do here in PORTUGAL. Ican get good semi-synts for 13$and do the job whell