The key is not to use something overly slick. Remember that the oil also lubricates your clutch pack. Too slick and you'll start slipping on the clutch too much and prematurely wear them out. If you use something way too thick it also tends to bog the motor down a little until the oil gets hot, the oil passages aren't like huge or anything so keep that in mind too.

Go with the weight the manufacturer recommends in a reputable brand and you'll be just fine.