Not sure what "fastest" means, but for what it's worth, out of all my SS7 platforms (and, boy, do I have quite a few), I achieved the greatest performance with two Asus P5A rev 1.04 boards.
Both of them are fast and rock solid at up to 115 MHz FSB (FSB can go even higher than that, but they are not 100% stable in all circumstances).
One of them (which is currently my fastest SS7 PC) has an AMD K6-3+ 400 overclocked @ 633 MHz (5.5 multi x 115 Mhz FSB) + GeForce 2 GTS, and the other one has an AMD K6-2+ 570, OC @ 616 MHz (5.5 x 112 MHz) + Voodoo 3 3000 AGP. Both of these are pretty incredible as far as SS7 speed goes, and can run games that I wouldn't even have dreamt of running two decades ago on my poor original AMD K6-2 500 MHz PC with a no-name board.
I'm actually searching for a Gigabyte GA-5AX, because I've heard many good things about it and I really want to compare its performance to the Asus P5A. Alas, I have yet to find one for a decent price. 🙁
2 x PGA132 / 5 x Socket 3 / 9 x Socket 7 / 12 x SS7 / 1 x Socket 8 / 14 x Slot 1 / 5 x Slot A
5 x Socket 370 / 8 x Socket A / 2 x Socket 478 / 2 x Socket 754 / 3 x Socket 939 / 7 x LGA775 / 1 x LGA1155
Current rig: Ryzen 5 3600X
Backup rig: Core i7 7700k