I've done my share of top ends, and tried virtually every oil out there from full synthetic to full fish oils. My personall preferance is full synthetic Klotz R50 @ 40:1 for racing, and 50:1 for play riding. Been using Klotz for about 9 years. The big benifit from Klotz (or any reputable full synthetic formula) is the absence of carbon buildup skunge on the exhaust valve mechanisms. You start running petro based mixes at the "rear fender sticker" recommended 32:1, and your valves will be gunkified in about 2 months. (strictly just my opinions and experiences).