IIRC Voodoo5 can benefit from faster CPU up to 2GHz, especially if you're using MesaFX or the likes to play T&L games on V5. Unfortunately, as SilentLoon has put, Voodoo5 AGP can only be put on AGP 2x slot (3.3V) --something Pentium 4 mobos do not have. Even when the AGP slot is not keyed, you still need to pay attention to the voltage supported by the slot; putting your Voodoo5 on 1.5V AGP slot can damage your card, your mobo, or both.
However, you can still use AMD mobos if you're to use Voodoo5 with CPUs faster than Pentium III. Here is some recomendations:
(1) Epox 8KTA3+. The mobo has AGP 2x slot, and supports CPU up to Athlon Palomino 2000+. Okay, the supported CPU ain't probably that fast, but the mobo has an ISA slot. Yup, this mobo has an ISA slot.
(2) Asus A7V333. Based on VIA KT333 chipset, this one also has AGP 2x slot, and if you get Rev 2.0 mobo, you can put Barton 3000+ on it.
(3) MSI KT3 Ultra2. Basically the same with A7V333, so it is a toss-up.
(4) Asus A7M266. Supports dual Athlon MP processor, so if you want to play Falcon 4.0 GLide with dual processor and Voodoo5 5500, this is probably the best choice. However, I'm not really sure if it really supports 3.3V AGP, so you may want to check with the manual.
Nonetheless, it is all back to your playing goals: do you want to push the Voodoo5 5500 to play newer games, or do you want to use it to play older games with FSAA? If you want to see how would FSAA work in older games like Interstate '76, then Pentium III 700 is probably too fast for your purpose.
On the other hand, if you want to use Voodoo5 to play new games, you need to look for mobos with AGP 2x slot that also support the fastest CPU possible. Asus A7V333 and MSI KT3 Ultra2 are favorites among the folks at 3dfxZone precisely for that reason.
Personally, if you just want to play 'newer' old games like Jane's USAF or the first Half-Life with maxed AA and resolution, I'd rather suggest Windows 98 and the fastest GeForce card that still supports it --and this comes from someone who has four Voodoo5 5500 AGP and five Voodoo5 5500 PCI Mac. 😉