I'm not posting this on smwcentral because I'm IP banned there (don't ask about it), but I still facepalm everytime I see a SMW hack with slowdown in it.
I've already found several code chunks that seem to need improvement.
-hex to decimal conversion
-some of the sprite drawing routines
Some of the work I started years ago, so I'll just have to post the code of what I already had. If anybody has a list of the most slowdown ridden enemies, you can post it here.