The 150r is pretty much the perfect bike for kart tracks. So I haven't see an 85 be able to compete with one, they are also hard to ride fast like most 2 strokes. but once you work hard at it and are able to ride it like it wants to be ridden you'll be much improved as a rider imo.
Keep an eye on the crank case. Tends to push oil over to the transmission side of the cases. Starving the crank of oil. You better breathe / vent the motor a lot. Spin it hard and, you will builds lots of pressure in the crank case causing what I have pointed out.
2 strokes rule for mini world, they are light and simple. We have rims for both models. I also recommend reducing compression and using big clearances.
