When I said Super Fast I meant full frame rate and butter smooth. No need to frame limit this game.
The weirdness continues but in a good way this time. As I mentioned in the other topic, dgVoodoo2 pegs this game at 1080x1920. With that said I could not get anything to work with dgVoodoo2. The best I got was the game running and doing a hard crash so at least I know I was hooking something. Then I stumbled upon ArcCabView which supports Sonic Dash Extreme. I don't know what black magic they're doing with their custom DLLs but after implementing that on my RTX2070 machine (the problematic one) not only is the game full resolution, smack in the center, but with JConfig it runs a lot faster! Not as fast as TP but very playable.
Remove all their dgVoodoo files and it's back to running like poo. Put the normal/official dgVoodoo files in place of ArcCabView and right back to a hard crash. So whatever the DLLs are doing that come with ArcCabView it's somehow speeding the game up drastically on this one system.
Some how a messed up DirectX install? Shrug.
There you have it. If you're having full screen issues and/or major speed issues running Sonic Dash Extreme with FULL resolution on a 4K monitor, set your scaling to 100% and check out ArcCabView. If you don't like the ReShade stuff you can turn that off.