My question is: do any of you with older Nvidia hardware experience VESA-related issues with DOS applications — for example with VBETEST.EXE or other VESA tools — that might benefit from NEWAX's additional fixes?

Hi,
Yes, I think it's somewhat unfair that currently the more buggy Kepler/Maxwell/Pascal cards with NEWAX loaded have a better VESA VBE implementation than older less buggy cards. 😀
E.g. my Geforce 6600 AGP is definitely affected by the function 4F06h related falsely reported scanlines /4 MB limit problem.

@Marco Pistella:

BTW, if we are talking about more generic Nvidia VESA Bios fixes: there is a long standing problem. According to VBE 3 specification there is the possibility to define the CRTC timings (CRTCInfoBlock struct) and load them together with a mode set with the help of function 4F02h (Set VBE Mode). Up until Geforce 4 (5?) Nvidia supported this extension and it worked perfectly. There was a DOS TSR (Unirefresh) that could be used to define at what refresh rate the different VESA modes should run.
But from (at least) Geforce 6 this function never worked anymore. Maybe it was the 1st sign that Nvidia was not going to add further VESA VBE features anymore but rather remove them.
This extension would be useful on CRT monitors where the high resolution VESA modes on BIOS default 60 Hz can present painful flickering.

I think if someone can restore this functionality, that someone is you 😀