There is the SIS496/497 newest revision (PR) that is stable with EDO RAM but the performance not better then with FPM because SIS496/497 isn't optimized for advantage of EDO memory.
A Tale of Two 486 Motherboards (ALi vs SIS)

My board is a Rev D board which has the pr revision

Depends on chipset/BIOS. There was a thread recently with different BIOS images for the Shuttle Hot-433 which I tried on my board. One of them contains an option to enable faster timing for EDO and it allows 3-1-1-1 at 33MHz and 4-2-2-2 at 60MHz (Cyrix 5x86 at 60MHz times 2). At 40MHz there was no benefit though, even a slight loss.

This is the only time I've seen an explicit option for EDO, and this particular BIOS has other problems: several of the settings have no effect at all and the L2 timing is permanently stuck at 2-1-1-1 (can't even be enabled at higher bus speeds).

Aren't there some other boards with UMC 888x chipset? Maybe after all these years we still need some BIOS hacking to unlock the full potential of these boards.

I got these results for memory read with the Cyrix 5x86:
33*3 FPM (0 wait) - 45MB/s
33*3 EDO (3-1-1-1) - 62MB/s
40*3 FPM (0 wait) - 54MB/s
40*3 EDO (4-2-2-2) - 50MB/s
60*2 FPM (1 wait) - 60MB/s
60*2 EDO (4-2-2-2) - 75MB/s

I did notice my Bios defaults the WT cache.. That reduces ram speed down to 40Mb/s @ 40Mhz bus