I always base my oil changes on USE, not miles or hours
If I am working an atv HARD< be it towing a food plot implement, or heavy things around the farm in dusty air, or even plowing a lot of snow,
its a LOT of added stress to a motor and its parts, so
I personally change my oil a LOT sooner, and I ONLY run SYN oil!
20 yrs of doing things this way and my atv runs like new and I have been very FAR from easy on it over the 20 yrs
IF your ONLY trail riding and not riding HARD and on the RPM"S a LOT, , if it was me, I would maybe go a little farther than the 600 miles, , maybe try going to 800 and then have the oil sent out to be analyzed?
and see what the test results say at that point!
BUT then again, oil AIN"T that costly
countless folks run Rotella syn and love it and get it pretty darn cheap, they also offer Rebates on it often too!
changing oil is way cheaper than motor work LOL
AT same time I also hope your NOT skipping out on air filter care here too!, running on a dirty air filter is not good either!
good washable one's are nice, get two, wash one and have ready all the time so when needing a change, your not waiting on one to dry!