Okay, here's my contribution.
As I see it, the only two places where dying could conceivably be profitable are
- after getting the key
- after getting the big key
which one did you try?
It is possible, as nitsuja said, that something that is faster in a speedrun (because it's easy) isn't faster with savestates and slowdown.
Around 49100 you take a very small detour to pick up arrows. You do not seem to need them, at least not in this dungeon. What are they for?
When lighting the beacons, they are placed like this:
A B
C D
You do them in the order DCAB, but geometry tells me that DCBA should be faster, because you end up closer to the door. Is it because of the enemy blocking the way, or the dash afterwards?
When mixing dashes with walking, you always do it perpendicular. Did you try with stopping the dash earlier and walking diagonally? Is it always slower? It feels counterintuitive, but that doesn't mean it's wrong. It might be related to the previous question too.
EDIT: The antlion can be killed with one arrow or one spinattack. Switching to arrows is slow, but did you try to spinattack it?