Is a Windows 9x issue on post Win9x board. That Intel INF file is not a driver but a pointer to identify the chipset properly. Many think the INF file has chipset drivers but it does not.
My guess is that the Intel i865 IDE controller needs a true proper 32bit driver for Win9x to perform well otherwise "it just works"...
added: If you still have the Win98 installed what does it identify the HD controller as ? If "standard IDE controller" that is why......

What are the controller settings in the BIOS?

cyclone3d wrote on 2021-05-26, 02:41:

What are the controller settings in the BIOS?

For the "On-Chip Serial ATA" the choices are Auto, Combined Mode, and Enhanced Mode. For Win 98 I tried Auto and Combined Mode, and I left it set to Auto when installing XP.

I reinstalled Win98, and since I don't recall having an issue like this with my P4P800 when I had Win98 on it while using its SATA ports with an SSD, I used the chipset installer for that board (Asus is great in that they still have it available to download). No change. I put in an IDE to SATA adapter, and disabled the SATA ports - no change.
When I first encountered this, I wondered if the drive might be at fault somehow, so I thought a good test would be to see if it worked with Win XP. But now I've circled back around to thinking that this drive doesn't like FAT32. Which I guess is understandable as only a tiny fraction of people would take a new SSD like this and try and use it with such an old OS, so they might not have bothered to see if its firmware was compatible with such an old OS.

What about trying XP with FAT32?

You could also try NTFS4DOS and see if that will let you install 98se on an NTFS partition.

Enable DMA access manually.

The Serpent Rider wrote on 2021-05-26, 10:22:

Enable DMA access manually.

That was the missing puzzle piece. Interesting that none of the Win98 installs I've done on various hardware over the past couple of years needed this done manually. Before I read that post I had put in an SSHD and installed Win98 on that with the same result. I enabled DMA in Device Manager and voila, drive speed was where is should be. I then reconnected the SSD and did the same thing with the same result. Thanks for the tip.

I ran into another issue, and in trying to sort that out I swapped in another hard drive, and did a couple of more Win98 installs. The problem turned out to be the optical drive was failing. In the process, I confirmed that with this motherboard/chipset and Win98, you have to manually enable DMA for the drives (both the optical and the hard drive) every time you install Windows 98.