Yeah, IMO PCI GeForces are worth snatching if you find them cheap. Usual suspects are the MXes,and FX 5200/5500, though AGP versions are much much more common of course.

The S3 Trios and Virges are strangely rising in price nowadays. Couple bucks, sure, but above $10... I don't think so...

For good 2D and 3D all-rounders, my short-list usually has the following:

- Nvidia MX200 and MX400 in PCI
- Voodoo 3000 and 5500 in PCI

The MXs can vary in output quality - some are just too 'muddy' looking.

I have a GeForce FX 5200 in my SS7 machine and I'm quite happy. It has VGA, DVI, Composite and S-Video and one of the few cards that clone the output under DOS.

I don't think I ran into many issues, the main one is in Wing Commander III, flickering when you move from room to room. Other cards don't have this issue, the V3 also has it, but the game has a compatibility setting that fixes it for the V3, but not for the GeForce cards.

A S3 Trio type card would also work well. To be honest I think that most cards work with most games, it's not like there are cards that break half of all the games.

Isn't the MX400 a 5V card, such that it might not work with all Socket 7 motherboards? I seem to recall encountering that problem many years ago. (Or was it 3.3?)

All the MX400s I've seen have been keyed for 5V. In any case most Socket 7 motherboards will provide 3.3V as it's part of the PCI 2.1 spec. Triton II certainly, I used a 430TX.
The earlier chipsets (LX/FX) might have PCI compliance issues similar to PCI 486 boards.

I read that the later PCI GeForces (GF4 MX4000, FX) might not work with UNIREFRESH so you're stuck with 60Hz VESA modes in DOS. Anyone found this?
GF2 MX - NV11
GF4 MX - NV18
FX5200 - NV34

From these informative posts it seems refresh rate control was indeed broken since the FX series on the Geforces

UniRefresh no longer works on nVidia's latest
LCD, fresh rate & DOS games
http://www.bttr-software.de/forum/board_entry.php?id=920

If you can get a socket 7 with PCI 2.2 which the later super 7 chipsets supported you can go up to say an 8600GT PCI card, though it might be overkill for your K6-3

My understanding is that cards faster than the MX400 might even run slower due to needing later/slower drivers. e.g. FX5500 is slower than the MX400 in some tests.

The TNT2 M64 is very good in DOS. Its weaknesses in 3D do not come into play in DOS, which means it's a less expensive option. I think most of the Nvidia cards from from the that era (Riva to GF5) were equally good in DOS. I seem to remember having an MX4000 that wasn't quite as good in DOS, but I don't remember the exact details (it's packed away now). I bet I can find it in an old post here.
edit: here it is
10 Way DOS Graphic Card Benchmarks on Celeron 333
these are AGP, though (except for the Voodoo3 2000)

In most cases you want a good all-arounder with solid driver support in Windows and good pure DOS compatibility, VBE 3.0, Univbe and unirefresh support. On nvidia side the older Gf 4x line and the Fx line are in contest. GF 4X are generally consume less power and might have some features (table fog?) that are absent from later models but I am hazy on this. On a super socket 7 machine the benefits of superior AA, anisotropic filters and pixel shaders kick in (oh yes, Max Payne's coat must shine:) and the FXs have the upper hand, although you might need to tweak the drivers with Rivatuner. With the FXs you want to use an Lcd, though.