I've been lurking and testing these in siege the past few days, and figured I'd post thoughts on some of the formulas. I use 90 vFOV hipfire, which is 81 vFOV in ADS, and I matched both of those 360 distances up as well as I could with siege's settings. I've tried every formula since the post with the wrong formula for 90 diagonal arc length for a couple hours. It might not be the best reference point but it's what I'm judging by personally. Also I use 300 dpi (usually) and have been using v2 from desktop for both sensitivities for a good bit now.
Anyway, these are some thoughts I had on the formulas that I thought might be useful (maybe).
I really liked the 2d to 3d from the 'bugged' diagonal 90 arch length formula, but it really was probably too fast.
The one drimzi said felt best going from 2d to 3d felt the tiniest bit slow for me.
"Viewspeed using Diagonal FOV" was very slow in comparison to the rest. Didn't match up at all to me, I don't think, even if it felt nice ingame.
Having spent time using v2, the "Viewspeed v2 / Chord/Arc" formula, which was the same as v2 at 90 vfov and faster at 81, felt better than v2 in ADS by quite a bit. However when testing with the ACOG matched (31.5 vFOV), it felt faster than I thought it should.
This new formula felt a tad slow to me at every fov, but I performed very well with it at all 3 FOVs and adjusted more quickly than I ever have, though I didn't quite lose the sluggish feeling at 31.5 vFOV. Both tracking and flicks (flicks to enemies on screen and also to doorways on and off screen) were great almost immediately. As good as or better than V2 / Chord/Arc, which is the best it's ever felt in ADS. After a few hours with it, I'm willing to bet the feeling of sluggishness just had to do with me being used to V2.
That's all from my notes I thought might be of any help as another data point. I'm not sure how final that declaration on the last formula that it should be super perfect is, but if you're not already there, I think you're definitely on the right track, and I do hope whatever ends up being the final solution ends up on the calc. Really cool to see people trying to continue to improve this!
Edit: forgot to just say that in general i think the newest one is the best overall. Going to try it in pubg soon, I think.