The main thing I noticed is that the last few screens look way more optimized than the first, showing you improved your strategy as you went along. For instance, on the first screen you hit the top koopa (the only one that matters in terms of speed) far to the left of the platform, causing mario to have to run all the way to the left to pick up the item then run back. Later you wait until he is at the edge; a more refined strategy.
As a test I did
a short WIP of the first screen. I think I could squeeze out some more frames but this gets into the pipe 59 frames faster than this submission.
I think this could use a bit more optimization. I'm not demanding perfection, but I do at least want there to not be a noticeable (to an average user) improvement in quality as the run progresses. I think the first levels need to be redone with the strategies used in the final levels.