I have an old Lenovo Thinkcentre M58 SFF (6258) which uses DDR3 and an old, highly customized non UEFI BIOS.
bought some Hynix RAM to increase the RAM amount but the the performance is not great due to SPD timings not optimized for that platform.
now there are two options:
1. modding the BIOS to introduce some sort of RAM timing options to adjust the latency
2. editing the JEDEC SPD data contained in the RAM modules to make them 100% compatible with the motherboard. I did that in the past using SPDTool but only for DDR2 while SPDTool is not 100% DDR3 compatible.
any experience or suggestion?

Link the BIOS, then we can decide, I may be able to make settings visible to you that you can't see now. Can you see any memory timings, settings, voltages?
SPDTool 0.63, or certain versions of Taiphoon burner are fine for DDR3, I've done plenty with both.

https://download.lenovo.com/ibmdl/pub/pc...ios/5cjt77a.zip

it is a highly customized BIOS, not the standard type at all...
I can see the timings with HWinfo, but there is no option in the BIOS.

Highly customized means nothing to me Sounds like it's highly lame and limited, if you can see nothing in BIOS, what makes you say it's special and customized??
It's very old and tiny BIOS, that much is true And yes, usually this old means not many settings, but it's still possible some may be hidden from you (at least maybe main timings)

Please run phlash16 or Winphlash and backup your current BIOS and send me that instead. All the tools I have for these older BIOS can't open the stock upgrade only file, so we need to see if I can view a dump properly or not.
You can try this WinPhlash version, it's latest, but unsure if it would work, you may need older version instead. I checked the included Phlash16.exe and it can backup BIOS, so you can use that but only from DOS or 32bit OS
http://s000.tinyupload.com/index.php?fil...276789813203172

If I can't the BIOS get it to open properly, then your only option may be flashing the SPD. I can send you SPDtool 0.63 and Taiphoon burner version that works for DDR3

it is indeed very limited, but definitively not for security and remote assistance: you can set 4 or 5 different passwords just in the BIOS!
but being a corporate machine it makes sense.
tried WinPhlash but it asks for a BIOS file even for making a backup of the existing one. I think working with the BIOS could be a dangerous path as the access to some functionality is relying on moving jumpers around.
will have a play with SPDTool, thanks

That's OK, makeup some name and try. Select backup only. BIOS mod would be fine, if it's possible, but I can't tell you until you send me backup.
If you can't get with Winplhash, use the stock included phlash16 (Extract stock exe and you will find it)