I currently only have one 386 board with a PGA socket. I used to have two others, but I sold them off. But you're right, there is the possibility that the board is causing the L1 cache problem....but I highly I doubt it.
As far as I know the TI486SXL2 33/66 was QFP only for 386SX and 486SX platforms (there wasn't one for 386DX), but it's available as PGA for the 486SX pinout (it's a 3.6V part).
The 144pin QFP 486SX part was sold on an adapter by evergreen or improve it technologies for 386DX pinout with VRM. I think a few people over on CPU world have them. I remember seeing one for sale on eBay a while back but I could never quite tell if it was for a 386 or 486 socket so I never went for it.
I haven't yet had much chance to do stability testing on my current board with fast timings, but it was quite solid on my ASI 386/486 hyrbid board I used to have. That board used the same chipset, but was much better with DLC chips if you could figure out the jumpers.
Try SXL overclocked using a lower voltage and see what happens. Currently I'm SOL.
"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium