First of all, awesome progress. I'm very impressed with your precision, especially the improvements in the pyramid. And also jumping off the key when first grabbing it was a nice idea and looks cool, even if it didn't work out all the way.
Watching your run, I think there is one other trick you might not know - hopping to keep your speed. When you stop flying by letting go of Y or by sliding into the ground (I haven't tested diving), you can time your jumps perfectly (meaning jump on the first available frame) and keep the same speed you would have kept had you been flying. The disadvantage to this is that you cannot press <- or -> because it will "reset" your speed back to walking speed. In my 15-exit run, I use it in most of Crystal Star World, which is why the screen does not follow me up at first - jumps on the first frame don't "count" as far as scrolling goes. I end up waiting an extra frame to let the screen catch up to me so I can clear the highest pillars. This was faster than landing and running back up to flying speed because my jumps are already at that same speed, without the slowdown of trying to re-reach that speed by running.
That technique on your run gives
this very minor improvement, at the end of Desert World 4, using this technique, and also the fact that you can slide into pokeys to kill them. I reach the goal two frames earlier, which I didn't even think was worth posting until I saw that it gained six more frames from the strange fadeout randomness. I also hexed your pyramid run thus far back into this run (which took a two frame delay to make it sync), so altogether this is six frames ahead.
The other thing I thought of was for a few levels down the road - Water World 1 really doesn't have much in the way of picking stuff up, so I thought "well maybe going back to the mushroom house and getting another shell to carry through the water would speed up things overall". The problem is that to walk back to the mushroom house from that area means you have to walk all the way around back to Desert World 2, because you can't walk from the pyramid to the house until you walk from the house to the pyramid. So, I give you this
other run, which hexed in an extra move on the map when you were at the mushroom house to make that option available, if it ends up being faster. Feel free to use either of these runs if you like.
My guess would be that the fastest option for the next few levels is the following:
Yellow Switch Palace
Desert Pyramid
#2 Castle (secret)
Desert Secret (for another shell)
#2 Castle
And then use the shell in Water World 1 (most of which you can swim under). It may even be worth it to get yet another shell to use again for the second exit to Water World 1 later on. The rest of the water levels either have stuff to carry, don't consist of all water, or auto-scroll (wheeee). So, none of this is tested, but I'm just bringing it to the table as a possibility.
Also the frame counts on the runs I have here are not exact - I just hexed in a larger number so the movie would still play through. That will fix itself automatically next time you work on the run, though.