Okay, so as far as I can tell, there is absolutely no different in movement speed between jumping high, jumping low, flying or walking, provided that you don't trigger any lag frames.
So I made it through the dungeon and back to the town, and now I realize something: by bypassing the fingernail and beating the 2nd boss, I'm now unable to obtain it at all.
The second bridge works like this: if you talk to the NPC without having the upgraded Wings, he steps aside. If you obtain the wings first, though, you have to fight him. This is probably why in the published run he talks to the NPC first, grabs the wings, then walks past him. This probably ended up being faster than fighting.
On a rough estimate based on watching the published run, the amount of time it takes to go into town the first time and get the fingernail is less than the time it takes to go back and get the wings (around 8 seconds faster). In addition, having the extra jump height saves me some time on the bridge and in the 2nd dungeon.
So... I'm going to have to redo this section. Oh well, at least now I know the faster route.
Regardless, I'll post my WIP here:
http://dehacked.2y.net/microstorage.php/info/1876602244/Gargoyle%27s%20Quest%20-%20Ghosts%27n%20Goblins.vbm
I did find a new trick just now, though. If you die after completing the 2nd dungeon (or any other dungeon, presumably), you respawn there after you die. By killing myself off after talking to the NPC in town I can teleport there which is possibly faster than crossing the bridge again. To optimize this I'd need to get into a random encounter as soon as possible though. So I'll have to do some investigation into the RNG.