The 3Dfx version runs like shit on my PC, the win95 patch is a bit iffy as well, so is there actually a way to change the resolution that the DOS software version is rendered at, or am I stuck with like 320x240?

Not sure, but I did find this:

http://www.carmageddon.com/forum/topic/11617

See the last post. It uses the switches "3dfx -novoodoo -hires" against the executable (change the autoexec DOSBox conf file for the game to launch the Carmageddon executable with these switches). It tries to use the 3DFX mode, but specifies that there is no Voodoo card present. It then tells the game to run in the 'hi-res' mode which might be 640x480.

But honestly, I'm not sure so you'll have to test this. I use the latest nGlide (1.02) and it runs fine with up to 1280x960 on my system.