For the Radeons you want the latest builds. In 2k that will be 10.2, and in 9x I think its 6.2 or 6.3. Table fog was not fixed in 9x, but is fixed in 2k/XP. Later drivers also will add TAA support for the X series card.

On the GeForces - usually 3x.xx or older is suggested for old cards, iirc its like 51.xx or thereabouts where they reportedly broke Lithtech. OTOH DVI RGB out range is flawed until like 167, but that can be fixed via registry hack (refer to release notes).

On the 6800, I think 92.91 should be fine. I've had good luck with 9x.xx drivers on GF7 at least. 71.89 has also been good IME, but unless you're having issues with the setup as-is, I probably wouldn't change.

Running 30.82 on my older Nvidia cards, works well thru VGA connector.

However if you want to use DVI, these drivers gave me problems in full-screen DOS prompts. I had to go to 45.23 to resolve those.

no its running on its own CRT, my 2000 and XP boxes monoplize the the LCD's VGA and DVI ports already, I really really really need a KVM 🤣

For Win9x/ME, the last supported Radeon driver is 6.2 - for the pre DX8 cards on later OS, there is 6.11 pre-R300.
For DX8 capable Radeons (9500 up to X and X1k) the last driver is legacy 10.2 - at some point in that sequence, they got multithreading - I think the history of that got lost with the driverheaven / hardwareheaven forum upgrade

I use 92.91 for all Geforce 6xxx and 7xxx in XP and have been doing so for ages. So far I have not found any reason for using another driver even if I have to admit I do not even remember why I did choose just 92.91. The only bad thing I have found with 92.91 is that its a beta driver which only matters if... nah it dosnt matter.

For NVIDIA, I just use the Detonator drivers, and for my TNT, all you do is go back 1 version from the Detonators.