I'd say keep Voodoo5, and try to silence it with quieter fans. There ain't much difference with speed at all, but the main differencies are that noise, and the following thing I'll paste here - it is my old reply to similar question in 2003:
There might be little difference performance wise between V3 and V5. However, there is one difference that I think makes Voodoo 5 more desirable.
You may well know, that Voodoo 3 supports only 16bit colors with 3D, while Voodoo 4 and 5 can use 32bit color screenmodes with 3D. With Voodoo3 you can't run for example Quake2 in window in 32bit Workbench. So you have to use "only" 16bit desktop if you wan't to watch demos/play (3D) games (in windows). This limitation makes also impossible to use your tv-card in a window (at the same time) with a game/demo on window too, 16bit is just not enough (without color corruption).
