What I did, in order to get my GeForce GTX 970 to be able to run my presets in their full glory at 4K was clone my preset folder and replace the MBZ__0__SMOOTH-ADV_GDV.slangp base preset with the MBZ__0__SMOOTH-ADV-NO-REFLECT__GDV.slangp.
Everything but the real-time reflections remain intact using those base presets.
I subsequently made some Standard Presets using Soqueroeu Mega Bezel TV Backgrounds and found that they didn’t need the smoothing as much due to them being scaled down to fit a smaller viewport. Then I used my Custom Blargg NTSC Video Filter Presets to take care of things like de-dithering and to smooth things out a bit more.
If you haven’t already, you should try them. They’ll have a nice post processing effect on your presets that you might actually like. They’re already in the RetroArch Video Filters folder.