sliding generally doesn't work out too well. The surface is course enough to provide sufficient grip to overcome the motors and just make them bog down. The light weight racers are able to pull it off but people with any substantial mass to them are going to lose speed while the light drivers race on.
It's a slightly different story with a set of drift rings on the back, but I still wasn't coming close to top speed while drifting around the track.

as for braking, some find they post better times w/o using the brake and simply letting off/coasting at the right points along the track. That first turn leading into the hairpins on The Dragon is probably the most important of the 3. Getting that sorted out will lead to better times and better passing opportunities while others fumble around with trying to figure out the correct line (or any line at all)