Probably a stupid question but if it's having difficulties running at full speed, a common trick is to split the operations over two frames. If the original pico 8 version is also 30 FPS, do youthink if that was done in this case, it might be full speed in C? How far off is it frame wise? It's difficult to tell from playing it. It seems faster than half speed.
I mean an easy solution that would help fix both the frame rate and and feel of the player physics would have been matching the originals 30fps frame rate, VBCC would be full speed basically everywhere except level 12 with as little as a 15% speedup. You can test overclock of the cpu in Mesen in scan lines and just divide by 525 for a percentage. Adding about 50 scanlines was enough to fix most slowdowns, though 80 was basically all.