This post will be a bit of a brain dump upon reading this thread to-date.
VLB slots on a 386 board only seem to be of performance benefit when using clock doubled CPUs. I recall there were some results in the 386 Speedsys post.
If you are looking for a 386/486 hybrid board, most of them have the 486 socket as well. To me, it feels a little lame to use a 386upgrade CPU, like a DRx2 in the PGA132 socket when you have a PGA168 486 socket sitting next to it. Very few of the 386/486-chipset-containing boards with VLB slots do not have the 486 socket, but some do. The UMC 481/482 chipset is a hybrid chipset. It is an OK chipset IFF you use the MR BIOS bios. There are plenty boards with this chipset which do not contain the 486 socket when it is ISA-only.
386 boards, in my opinion, are the most difficult to work on. There are so many flavours and they are quirky when paired with SXL2 and DRx2 CPUs. You have to be willing to dedicate a lot of time to figuring out what combination will work.
For the most part, an SXL2-50 will run you around $80, perhaps double or triple for a DRx2-66. For the most part, these quantities probably pale in comparison to your daily salary and if you are really passionate about the hobby, probably won't hinder you much. There are even faster upgrade options for the 386 socket, such as the BL3-75/100 on interposer and SXL2-66 on interposer. These are particularly difficult to find and may require years or decades of searching, the latter of which I may have just acquired.
If going for a board with a VLB slot, it seems much better suited to use a proper 486 board with VLB slots.
keenerb, did all versions of Scorched Earth use a math co-pro? Would be interesting to see a video of a system with and without a FPU playing that game.
If you are after a real 386 board, that is a board which does not contain a chipset which went both ways, and are wanting the best performer, the SiS Rabbit and VLSI, I think its called 'Tomcat', are the way to go. They sport do require software to enable the L1 cache though. On all boards, you need to play with the cacheable range and holes setting, especially when using SCSI DMA cards.
For hybrid boards with VLB slots, there are some interesting results in this thread. Start reading here: Re: Post your 386 Speedsys results here
dirkmirk, how far did you get with the overclock of your SXL2-50? I find 55 MHz to be the ceiling for stable performance. Use a cooler. I hoped that the IIT x2 50 MHz FPU would also run stable at 55 MHz, but it would not. Looks like a lot of these clock doubled chips were at or near their design limits.
If you get a board with a C&T CHIPS chipset, of all the examples I've seen (2 from me, plus 1 elsewhere), none of them were able to use 256 K properly, even though they have jumper settings and sockets which allow for 256K. On one of my boards, 128K was max, and 64K on the other. I recommend boards which support double-banked cache as these tend to interleave the cache, allowing you to use faster timings reliably.
Much time has elapsed since this thread started. Jupiter-18, what did you end up sourcing and putting together? If it were me, I wouldn't skimp on any of your desires, because, later on, after you have a system up and running, you may be left yearning for more. If you are fully maxed out, then the yearning on that particular platform will subside and you'll be left with a feeling of completeness. If you skimp on features now, you will likely have to buy more later, which requires further cash expenditures.
Plan your life wisely, you'll be dead before you know it.