hello, i have a fs650 2008 that i use for racing , and also for commuting.
i always use 10w40 of any brand of any kind semi-synthetic in my engine since new.
change oil every practise or race or at maximum 5 hours of operation.
270 hours now at the clock and never had an issue, not even worn piston rings, not even worn rocker rollers not anything which is connected to lubrication issue.
at the moment , as i bought a box, i use repsol 10w40 , 6 euros per bottle :bounce3: