There are a couple of recent(?) discoveries that should be known to anyone planning (or already secretly working) to improve either Mega Man X2 run. I wasn't sure if these were commonly known but I asked a couple of people on IRC and it sounds like most people don't know about them yet, so I'm posting here to make sure nobody misses them:
Crystal Snail miniboss skip using S. Burner and arm parts only -- see edit below for low% (snes9x 1.51 smv, I typo'd on the microstorage comment)
On the walkway leading up to the miniboss, simply do a dash into a charged s. burner. There's a fairly large window of opportunity to execute it. This does NOT work on 1.43 but it works on 1.5x and (importantly) it works on console.
Double jump with arm and leg parts (snes9x 1.51 smv)
When you've obtained arm and leg parts, you can perform a double jump like this: fully charge your buster (release fire at some point before or during the trick, you need the stored charge for this), then do a non-dash jump, followed by an air-dash, then press fire and jump at the same time and you'll jump again from mid-air. This can also be performed off of a (non-dash) wall jump. This works on all snes9x versions and on console.
(smv's using Mega Man X 2 (U) [!].smc)
Major edit:
It's also possible to
skip the crystal snail miniboss in a low% run with s.burner by firing an s. burner along the ground while dashing.