I'm a previous user of the modded BIOS for T-420 (1.51 (83UJ32US)) and T-520 (1.48 (8AUJ29US)) which had the white list removed and displayed the Advanced BIOS settings. These have worked wonderfully well.
Unfortunately, one of my T-520s lost a motherboard, and I accidentally ordered a W-520 motherboard with the Quadro 2000 GPU by mistake. It does fit the T-520 frame, and will take 32 GB of RAM instead of 16 GB (which works for me, although it needs a different fan/heatsink, DC power socket and a 170 W power supply), so...
I've decided to keep it *IF* I can find the W-520 1.46 (8BUJ25US) BIOS mentioned above at
http://rgho.st/8JBjMm4mn (which appears to have had the file removed).
Were the T-420 1.52 (83UJ33US) and T-520 1.49 (8AUJ30US) BIOS available as well, I would be interested in those too to update my other systems.
If anyone has information on what the Advanced BIOS options are (more than just going into the BIOS and looking at the brief, but at times not too helpful, descriptions, I'd be interested in that as well.
My thanks in advance for any leads on this.