X1 Carbon (Haswell) performance boost due to unlocked tdp

Unhappy with the severe tdp throttling of my X1 (4550U) under continuous stress I have been trying for weeks to improve CPU/GPU performance using Intel XTU and throttlestop to no avail. I came to accept that haswell ulvs are throttling by design:
http://forum.notebookreview.com/hardware-components-aftermarket-upgrades/751935-haswell-ult-throttleing-design.html
But now, miraculously tdp (or turbo boost power time window) became unlocked (no clue what I did except the usual fumbling), which results in a significant performance boost.
Here are the 3dmark benchmarks:

5004 Cloud Gate
3051 Sky Diver
768 Fire Strike
48111 Ice Storm
According to XTU tdp was around 20W.

Please compare with the results measured by notebookcheck with tdp 15W:
4360 Cloud Gate
658 Fire Strike
35290 Ice Storm
Test-Update Lenovo ThinkPad X1 Carbon Touch 20A7-002DGE Ultrabook - Notebookcheck.com Tests
In games like GTA IV this 15-35% difference is pretty noticeable. I would love to enjoy this performance permanently, but I am pretty sure that a reboot will reset the tdp state or turbo boost timer (as once before), since Lenovo locked it in the bios. Why did they choose to do so? Is tdp 20W dangerous?
I don't think so, because according to XTU CPU temperature never surpassed 75 degrees, which is way below the thermal limit. Furthermore the system has been running stable for two weeks. During this time I have been playing GTA IV extensively without problems:

Why can't Lenovo give its Thinkpad users more control over the CPU so they may enjoy this performance at will?

 

It's only 5 Watt. Don't worry. As long as you don't put high loads on the CPU for a longer amount of time, you should be fine.

Undervolting does not work. I was unable to apply 25-50mV undervolts on mine. Crashed immediately. Seems to work on full voltage CPUs though.

 

Pretty good results. I'll have a look at these settings again. Uninstalled XTU because it's service is a CPU load waste. Instead I use throttlestop to undervolt my 4550u with approx -77mV. Idle voltage is about 0.605V and full cpu load at 0.930. My CPU seems to have a high default vid.
Because of the thermal limit of 15w I also squeezed a bit more performance out of the machine.

 

Yes, undervolting appears to be the only "regular" way of tweaking performance. I will have to stick to it, too, for unfortunately the unlocked tdp effect did not last. After a couple of reboots I am back to normal. Lag, here we go again.

 

The crash isn't too surprising, seeing as Intel already undervolted it (ULV stands for something).