for all intents and purposes the WR is 1:42 by AC: https://www.speedrun.com/ssol/run/yj69r8gz (it's using the speedrun-mod client -- the physics are the same, time is measured in ms, there's an inbuilt timer with custom splits, and more).
SSOL is a pretty harsh game wrt inefficiencies -- a small error about when to slow down can mean losing a second or two. The route that AC uses was the best route that AC and I independently found (he capitalized on it, I didn't). Is there a better route? If not, then (excluding glitches) maybe a little under 1:40 is the realistic best, but there's room for it to go lower with a better route.
AC and I used a map of the level (overhead shot via unity decompilation) to find routes -- IDK if that's still around in discord, but it should be in my strats and analysis video (tho probs always with some stuff on top of it). We used path length as a way to find shorter routes, you can use something like inkscape or illustrator to do this (this method isn't perfect -- doing a 180 in SSOL is expensive, but smaller angular changes are often okay; path length doesn't account for the change of direction).
