what consumers had access to by walking into a retail computer dealership (there were many independent white box makers at the time) and saying "give me your best."
You're probably right about me underestimating the graphics, though it's hard to remember back that far. I'm thinking 800x600 was much more common. If you could get 1024x768, it was usually interlaced (i.e. "auto-headache") and rare if I remember correctly to be able to get with 24-bit color—S3's first 16-bit capable chips didn't come out until late-1991, if I remember correctly, though I could be off.
SCSI was possible, but almost unheard of as stock, you either had to buy an add-on card and deal with driver/compatibility questions or one of the ESDISCSI bridge boards or similar. Same thing with ethernet, token, or any other dedicated networking hardware and stack. Most systems shipped with a dial-up "faxmodem" at the time, and users were stuck using Winsock on Windows 3.1. It was nontrivial to get it working. Most of the time, there was no real "networking" or "networking" support in the delivered hardware/software platform; faxmodems were largely used for dumb point-to-point connections using dial-up terminal emulator software.
And in the PC space, the higher-end you went, the less you were able to actually use the hardware for anything typical. Unless you were a corporate buyer, you bought your base platform as a whitebox, then added specialized hardware matched with specialized software in a kind of 1:1 correspondence—if you needed to perform task X, you'd buy hardware Y and software Z, and they'd essentially be useful only for task X, or maybe for task X1, X2, and X3, but certainly not much else—the same is even true for memory itself. Don't forget this is pre-Windows95, when most everyone was using Win16 on DOS. We can discuss OS/2, etc., but that again starts to get into the realm of purpose-specific and exotic computing in the PC space. There were, as I understand, a few verrry exotic 486 multiprocessors produced, but I've never even heard of a manufacturer and make/model for these—only the rumor that it was possible—so I doubt they ever made it into sales channels of any kind. My suspicion (correct me if I'm wrong) was that they were engineered for particular clients and particular roles by just one or two orgnaizations, and delivered in very small quantities; I'm not aware of any PC software in 1992 timeframe that was even multiprocessor-aware, or any standard to which it could have been coded. The Pentium processor wasn't introduced until '93 and the Pentium Pro with GTL+ and SMP capabilities didn't arrive until 1995. Even in 1995, most everything was either Win16 or 8- or 16-bit code backward compatible to the PC/XT or earlier, and would remain that way until around the Win98 era.
The UNIX platforms were standardized around SCSI, ethernet, big memory access, high-resolution graphics, and multiprocessing and presented an integrated environment in which a regular developer with a readily available compiler could take advantage of it all without particularly unusual or exotic (for that space) tactics.