The way I see it is like this: for an average texture mapped 3D
game (such as NASCAR, IndyCar Racing, Grand Prix 2 et cetera),
about 90% of the processor load goes on graphics. The other 10%
accounts for the aspects of the game such as the physics model,
driver AI, timing, collision detection etc.. In theory, a
3D accelerator card has the potential to remove virtually all
of the 90% graphics overhead from the CPU - which would give
your 486 with 3D board superior performance to a Pentium based
machine without.
The reality, as it stands at the moment, is slightly different..
The first generation of 3D boards (eg the Diamond Edge, 3D
Blaster) are pretty primative. In reality, the Diamond Edge
can't push Virtua Fighter Remix around at the target (30 fps)
frame-rate even on a Pentium machine (all detail on). Apparently,
the performance gains people have seen out of the 3D Blaster
are 'noticable', but certainly not very significant.
My advise is to leave buying a 3D card for about a year, by
which time a host of significantly faster (and PCI based)
cards should be available (such as the #9 card which is going
to be supported by Quake). As of now, I would advise you to
upgrade to a Pentium based machine, to give you a good, solid
platform from which you could later upgrade with a 3D card.
Fraser