Just tried the new build and it's just as laggy as before. Also, the steam build doesn't really help me as I'm not a steam user . . . as evident by me being here on Itch.io instead of on steam.
The new optimizations don't seemed to have improved things at all. And no, i don't mind sharing my PC specs at all. What would you like to know?
Also, while I'm down here typing this, the music from the game is playing without skipping so maybe it's a visual thing or an Itch integration that's causing the lag.