I don't know what can be done to resolve this issue if you are experiencing lags on auto and quick saves (other than disabling auto saves and not using quick saves). I was experiencing lags of 15 to 20 seconds using a STEP 22.214.171.124 Extended setup with vanilla ugridstoload. The only difference between my setup and standard STEP 126.96.36.199 Extended is that I had installed XPMSE instead of XPMS and I'm using the higher resolution meshes and textures.
One point that is noteworthy is that Neovalen has never experienced these lags and his setup is way more complex than STEP Extended. I know he use the higher resolution meshes and textures as well.
I plan to revisit this at some point in the future, but I haven't had time to get back around to it yet.