Over the years, everyone here has pretty much agreed that the Yamaha stock belt is the best to run.
According to the service manuals:
'92, '93, '94 750's run part number 89A-17641-00-00
'95 800's run part number 89A-17641-10-00
'96 800's run part number 8BU-17641-00-00
'97 800's run part number 8BU-17641-01-00
I have also run Dayco Ultimax belts for years and have never had a problem on the trails, but I don't push it as hard as the guys who race their sleds.
Nowadays, you have to run the 8BU-17641-01-00 on all Vmax4’s regardless of secondary. That’s all you are likely to find. They will work perfectly. The secret is to clutch accordingly to insure the clutches grip the belt hard enough; usually add weight. These are very “hard” belts, hence they are really durable. Been doing this for years.