If Descent has obvious texture pop-in it will be because the in-game detail settings are turned down, not because of the machine's performance.

I am having a similar problem on a P3 500MHZ system with 256MB memory and a PCI GeForce FX 5500, I use DOS 7.1, this computer only has ISA and PCI slots, I found out that using an ISA card will slow down a PCI card on this computer, but even when using both a PCI video card and PCI sound card, I was still getting a strange "surging" of speed and then a split second of slowness, one game in Windows 98se shows this off pretty well, Unreal Tournament 1999, I can run and move in the game with a full frame rate but then suddenly every few seconds the game slows down and drops to about half or less the normal frame rate and then almost instantly it's back to normal, I have the same problem on another computer, this other computer has a VIS C3 800MHZ CPU with 256MB memory and a integrated UniChrome video, the only similarity between the computers, other than the software they run, is they both use an SD to IDE adapter, and I think that's what the problem is, I am going to try to fiddle with SmartDrive and other disk caching and disk buffering software and settings to see if I can fix the problem.

I've never used QEMM (since I was always able to use DOS 6.xx's HIMEM.SYS & EMM386.EXE effectively to maximise my available memory).
The only change I would recommend is to remove the "DOS=HIGH' string from the 2nd last line in your Config.sys file and just amend the line at the top that currently states "DOS=UMB" to "DOS=HIGH,UMB".
Also, have you tried to "rem" the last line in your Autoexec.bat file (the one that has "fastvid" in)?

In the command prompt, type mem /c |more and show us a screen shot of that.
Regardless, I tend to agree with jmarsh - I don't think it's because of theconfiguration of your setup files.

will1384 wrote on 2020-06-21, 19:07:

I was still getting a strange "surging" of speed and then a split second of slowness, one game in Windows 98se shows this off pretty well, Unreal Tournament 1999, I can run and move in the game with a full frame rate but then suddenly every few seconds the game slows down and drops to about half or less the normal frame rate and then almost instantly it's back to normal

if this happens in windows games specifcially it could be due to vsync being on in the drivers. also smartdrive is not needed in win9x as vcache replaced it. i would also make sure to enable dma in device manager, if possible.