I don't know if you are driven by a need to mess with random hardware, or if you just want to game, but I would go with 815 without a second thought. VIA is definitely not on the same quality level.
Use as much CPU power as you want. Very few Windows 9x games are negatively affected by extra CPU speed. There are even SVGA DOS games that benefit from maximum CPU power.
And use whatever GPU you like. 5900 is nice and you can run one with even a K6 if you so desire (if the flaky Super 7 board will behave). For DirectX 7 games, unless you want 1600x1200 or higher and 60 fps, a 5900 is unnecessary. Ti 4200 will most likely satisfy. It's certainly vastly faster than Voodoo2 SLI.
Also you might like the site some of us worked on.
http://www.vogonswiki.com/index.php/Main_Page