A lot of the more powerful brushless systems seem to be sensorless. Its too bad really since the sensorless system is mainly for boats and planes that don't need the smooth throttle response that car/trucks need. We need manufactures to start coming out with more options for sensor based brushless. One of the major factors in using brushless is that it is more efficient compared to a brushed motor. Running a sensorless brushless is kinda like runing a motor without a timing belt or other timing system. You can do it but you lose performance and efficiency - both of which are important in R/C (I know I never seem to have enough power or battery life
I really have to give props to Novak on their 5800 system. Its not the fastest but there is a lot to be said for the other features a sensor based motor provides. I went out bashing this weekend with a friend and his T-Maxx. We were heading out to a new bashing site but the grass was too long so we decided to stop by some rocks we saw down the hill. I had my 'pede set up for 21/87 for some speed (wanted to race his nitro - did pretty good against him 'cept keeping it straigt was a bit of a challenge . I haven't been out rock crawling but this place was absolutely perfect so I had to see what could be done. I didn't change the gearing - just wanted to see what it was like the way it was set up. I was very impressed. I was crawling up rocks that I thought I would never get up - the control on the motor was awesome - smooth as glass. The T-Maxx was screaming like a banshee when it tried to crawl. For a change of pace I would get off the rocks and fly down the road at break neck speeds. Come back and crawl up the rocks again at a snails pace. I also managed to get 20+ minutes out of a 3000 mAh Viper pack non stop crawling/racing. This is something a sensorless could not do - the cogging on the rocks would be painfull at the least. With the sensor based brushless I can almost go anywhere in my 2x4 'pede that my stock E-Maxx can go with 4x4.
Its too bad there isn't more powerfull sensor based brushless out there. Hopefully we will see a trend towards sensor based!