I have briefly tried each release of the beta drivers since 1.04.9c was out, but the problem is the beta drivers usually have poor OpenGL performance and you will find your Q3 performance drop from the normal WHQL drivers.
However I have been using the beta 1.05.01 drivers and they actually run Q3 the fastest from all of the drivers, and in about 2 months I have have had one crash. I think the release date of these drivers is 17 July so you can find them in the "archives" section of the drivers page.
There are reports of certain P3 and AMD systems refusing to boot afterward so make sure to read the readme before you download the drivers and install them.
Think about what your reasons are for using the beta drivers. If you don't really need them don't take the risk, although as I said I haven't had any problems with them. But remember your system may be different to mine.
My system is:
Intel Celeron 500
192 MB 133 MHz SDRAM
3dfx Voodoo 3 2000 PCI
Microsoft Windows 98 SE