It does appear to run without glitches. But your comment indicates that you never played the original Quake. Which ran at 60fps, software-rendered, on a Pentium I, with no audio latency.
At half the resolution this is running at though, and the Flash does benefit from quite a speed up if you knock down the viewport size.
I have to disappoint you - I played original Quake on Pentium 133 running at 38fps, software rendering, without any glitches.
As far as I remember - not many things were running slow at that time - it was either you had the hardware to run stuff, or not.