In the middle of the 3 jumping slopes, it's faster if you just don't jump. Keep boosting as if you were on the floor. You also get the rings of the 3rd jumping slope consistently

Major improvements left: flawless cave

Minor improvements left: better jump at the first jumping slope. jumpboost glitch inside the icicle cave. Picking up 3 rings at the start.

At this point I have assumed that every world record of mine will have the visit of a friendly Boo passing by the bridge to say hello, how nice of him