I purchased the game with when using my old GTX 760 card and got a fair ways into it, but upgraded to the RTX 270 Super and haven't got it to start since. Nvidia doesn't seem to care enough to make a game-ready note for it, and am wondering if anyone here has got it up and running?

I tried the trick of changing the startup string to: "C:\Program Files (x86)\GOG Galaxy\Games\DOOM 3 BFG\Doom3BFG.exe" +set r_fullscreen -1 +set r_windowHeight "1440" +set r_windowWidth "2560" +set r_windowY "0" +set r_windowX "0"

and then I get console barf including:
"Unknown command 'vid_restart'" and it goes nowhwere.

ANY ideas? Am thinking I might have to buy the XBox 360 version just to finish the game! ;0p

That sounds like a driver issue.
Have you tried to put the resolution +1 of what you have it?

Solution:

On the game page click on [=] button next to [Play}
Manage installation
Configure
Features
Duplicate file 1
Paste agrument to created File 3: +set r_fullscreen 1 +set r_windowHeight "1080" +set r_windowWidth "1920"
OK

Done

Adding only +set r_fullscreen 2 worked for me

Try running with RBDOOM-3-BFG or DOOM BFA

https://github.com/RobertBeckebans/RBDOOM-3-BFG
https://github.com/RobertBeckebans/RBDOOM-3-BFG/releases


https://github.com/MadDeCoDeR/Classic-RBDOOM-3-BFG/releases/tag/1.2.8-BFA