Just doing 2x Upscale from any lower resolution is almost unusable. It starts at 30/fps and before 3% is processed it drops to anywhere from 0.1 to 4.0. A couple weeks ago I could upscale 30 minute home video in about an hour. Longer videos still averaged about 2 times their play length, but depending on the original quality, up to 4 times.
Generally, I am taking the defaults, selecting 2x upscale, and Proteus.
The dev team has been looking into issues with drops in performance that were seen in v5.5 and carried over into the latest release of v6.0.1. A patch update is forthcoming and should help to resolve this issue in v6.