On that card, you can enable the extra RAM only from the BIOS.
Try one from here:
https://3dfxbios.cl-rahden.de/index.php?title … o4#Voodoo4_4800
Or, you can edit the regular BIOS.

Increasing the video card memory from 32MB to 64MB unexpectedly caused a 3-4% decrease in performance. Also, in some game episodes, textures were incorrectly painted. This manifests itself in the same way - both with the reference drivers and AmigaMerlin. I did not see any advantages in the Voodoo4 64MB option. Perhaps I am doing something wrong and made a mistake.

In UnrealGold, incorrect texture shading rarely occurs, but in Quake2 you can see a strange picture almost all the time

Try with this driver LINK

I have one of these modded cards too. I remember having some issues in the 3DMark texture test initially, I think... it was like 15 years ago 😁
But in actual games, there were no problems then and the card still runs fine today. As for the performance - I didn't notice any performance reduction. Only increase in some specific cases (quite rare).

The easiest way to test performance of 32MB vs 64MB Voodoo4 is probably 3DMark 2001SE. You should see some measurable improvement of the score - 100 points or something.

Regarding drivers - for Windows 98 and VSA-100 cards, I use pretty much always use 3dfx Voodoo4/5 V1.04.00 -> https://3dfxarchive.com/vsa100.htm Also you can enable AGP 4x mode in the 3dfx tools, this might increase the performance slightly.