Please help me make lemonade with my X1 Tablet G3 Lemon - BIOS & Cooling!

Hi all.. multiple issues I'd appreciate any help with. This post I'm asking for some BIOS help please!

I'll get this out the way now: yes, I screwed up - November 2018 I bought a custom 20KJ X1 Tablet Gen3 with all the bells and whistles, including the terrible cooling and consequent strangling of my 8550U, the defective screen coating, the buggy FPM and flaky keyboard. 16Gb 2133 RAM and 1Tb SSD.
OTOH I needed a tablet format on the go, with TB3 docking and eGPU at home, and it really was the only option except Yoga (which would have been a better purchase given the problems...)

After a mobo replacement last year from crapped out TB3, I was having severe thermal issues.
I contained the problem with the excellent fruit of @unclewebb 's loins, Throttlestop - I've been deep in registers, VRM specs, and HWinfo CSV exports for two weeks and have repasted and partially dealt with THAT problem, I'll go deeper into that later..

For now, however, whatever I do to help along the anaemic thermal solution, I'm still gonna be stuck with Lenovo's utterly restricted BIOS that seems to enjoy running my BCLK in a range of 99.76-99.81 rather than the 100 that would actually give me the 2133Mhz memory speed and 4GHz CPU top end I actually paid for.
And that's apart from all the other monstrosities that Lenovo seems to have done in this BIOS to contain the heat/fan problems of this spec, and generally to technically castrate the user and limit the ability to do anything beyond turning off the internal battery (which with this model is proving sadly very uself)..

Sooooo anyone out there have a good lead/already have/point me in direction of a less restrictive BIOS for this rig that would get me full access to the meagre options I did actually pay for? It's currently on v1.4...
I've searched far and wide, and can't find anything on the wild wild edges of the internet, beyond asking for a custom mod.. I'll go that route and offer a prize too, if I have to, but maybe some kind NBR guru aleady has a solution on hand.. If I hazard a guess I'd say a BIOS from the 3rd Gen Yoga might also do the trick as the H/W is identical
Ideally, I'd like to fix BLCK at 100, at least disable this variable thing it's doing, preferably set my memory timings myself or at least fix them at the rated spec for the MT52L1G32D4PG part, and if the BIOS would allow me to set multipliers (lower, yes, I know), power limits and voltage offsets there that would of course be bonus land...
All pointers/help appreciated, I'm comfortable with anything short of replacing the BIOS chip

Cheers
J