the double wing strat grew on me quite a bit. The obvious use of it in E4 is to grab two wings at the Blockhouse and skip the entirety of the Ambulatory.

However, what I have been trying is grabbing wings at the Ambulatory as well (very close to the exit), then opening the secret area in Sepulcher and grabbing the wings there in order to skip vast majority of the Grand Stair.

So far, I found that both wing route and non-wing route tally to basically the same time (the time loss at Sepulcher is equal to the gain from Grand Stair), as long as you go through the green door, lower the blue key and then return for it using the chaos device.

Until now, that is. If you snatch the blue key as in the video, I think there might be solid 10 seconds to be gained. My problem is, I find it very difficult to pull the key snatch off quickly and consistently. I would be interested to hear how complicated you guys find it and whether you have any tips on the setup.