have this OEM board with the neptune chipset, which of course doesn't offer any real tweaking options in the BIOS, and decided to try out tweakbios 1.53c on it. compared to 430LX, 430NX has faster timing options for DRAM burst - x-4-4-4 read/x-3-3-3 write and x-3-3-3 R/W. though, if i read the datasheet correctly, even the default x-4-4-4 should be one clock faster than on 430LX. anyway, changing this from x-4-4-4 to x-3-3-3 improves memory bandwidth in speedsys 4.78 from 90.37 mb/s and 38.38 mb/s to 112.94 mb/s and 44.22 mb/s. pcpbench also improves from 11.8 to 12.1 FPS (p90, matrox millennium). so for a chipset that's usually derided as slow, i'd say that's still a welcome improvement. VESA transfer speed in speedsys stays unchanged at 36 mb/s though, and as i've mentioned in another thread, i'm not able to get fastvid's vspeed to work with these chipsets.

tweakbios offers two more settings that seemed of interest - burst refresh and refresh type, which are at disabled/RAS only in the BIOS. the help text says CAS-before-RAS is faster, but i'm only able to change it to RAS-before-CAS - not sure if that's a typo. changing both did not affect anything, though. all the other performance settings already seem to be at the fastest. right now, the board has mixed 32mb mixed 60/70ns parity RAM. can the x-3-3-3 burst setting be expected to work reliably with this?

finally, since tweakbios is changing these control registers after boot, i'm wondering if there is any reason in terms of stability to flash these settings to BIOS instead of just putting tweakbios into autoexec.bat? the only phoenix bios editor i found is from 2006 and doesn't even run under DOS, so i'm not sure if this would even work for a board that old.

edit: did some more benchmarks on this, changing only the one setting to x-3-3-3:

doom (doombench method, no sound): 54.16 FPS -> 55 FPS
quake (1.06 no sound demo1): 21.8 FPS -> 22.7 FPS
duke3d (dukebenctim.txt method): 45 FPS -> 47 FPS (320x200), 20 FPS -> 20 FPS (640x480)
shiny 1.4: 42-43 FPS -> 43 FPS
cachechk v4: 55 mb/s -> 61.9 mb/s, read 152 ns -> 135 ns, write 237 ns -> 203 ns

so in terms of DOS games, only quake is even remotely close to be able to use the extra memory bandwidth. also, though i can't easily boot to memtest with this tweakbios setup, quake is stable enough to run a good hour with this. by the way, this is the second board where this CTCM7 tool completely fails, it just hangs with some flashing lines (can still ctrl+alt+del out of it at least). suspecting this tool might not work with the matrox millennium for some reason - or, this is too new a version that was only tested on later platforms.

edit 2: found the "refresh type" in the spec sheet, where it says that on 430LX, CAS-before-RAS is not to be used with regular non-burst SRAM cache, but 430NX lifts that restriction. there is only one bit for this setting, so just the two aforementioned settings, meaning that this must indeed be a typo in tweakbios. but the setting did not show a difference anyway.