How would it not run faster, given that otherwise CPU had to shoulder the rendering entirely, in addition to everything else? Even high-end CPUs at the time would struggle with that, especially with resolution and bit depth being equal. IIRC the original Quake didn't even allow more than 256 colors in software rendering for this purpose, and even then I recall having to run it in weird resolutions like 400x300 to get framerates comparable to what Voodoo owners had for 640x480x16bit.