[Nexus 5X General] Razorless:
Disclaimer: I'm not responsible if you are not careful and fry your phone!

Updates and all the newest information:

Update: Disabling core control disables hotplug management altogether. If the big cluster is offline, turning core control off will cause the bigs to remain offline forever. Likewise, if the bigs are online and you turn core control off, then the bigs will never shut off. Throttling temps are not affected by core control.

As suspected, msm_thermal seems to not do anything on the Nexus 5X.

This was tested with elemental kernel and EXkernel manager. I don't know how this works on other kernels.

I ran a benchmark with BOTH msm_thermal and core control disabled and the CPU still throttled and shut off at the values specified in the thermal-engine.

That means that msm_thermal most likely doesn't do a thing on the Nexus 5X update: msm_thermal seems to be overriding the below values with "infinite". Additionally, all that core control does, as long as it is enabled, is overriding these two lines in the thermal engine:

[CPU4_HOTPLUG_MONITOR]
thresholds 41000
thresholds_clr 39000

and the same for CPU5.

update, important: For anyone not wanting to take (larger) risks but still wants to utilize the big cluster more: I attached a modified thermal-engine at the bottom of this post. Rename it from "conf.txt" to ".conf", place it under "/system/ect" and overwrite (backup first) the existing file. Set permissions to "rw- r-- r--" then reboot.

This setting uses the big cluster at max high speeds until shortly before the small cluster would be throttled. The sustained performance under medium load will be much better, but the phone will heat up faster. However, the maximum phone temperature will not increase.

Note: This is not the best setting for gaming or other heavy load. Your phone will throttle the little cluster a lot sooner. This will also drain your battery faster, but gives a better performance.

I ran some quick tests, changing the values

[PID-BIG_CLUSTER_management]
set_point 39000
set_point_clr 37000

immediatly affects the throttling temperature of the big cluster, no reboot required a reboot is required. Simply changing the temp does not affect the behavior of the PID algorithm, it just raises the starting threshold. The same goes for little cluster and GPU.

update: new information regarding thermal limits of Moto X/MI4C/Nexus 5X

update, exciting!: As [MENTION=4440904]GoldGanja[/MENTION] pointed out in this post, we might be able to raise the real throttle temperature of the big cluster

The original test for sustained frequency of the big cluster may be inaccurate, because the thermal management temp (still not sure which one it is) could have been higher/lower update: outdated, throttling temperature does not effect how long the big cluster is utilized, see below for details

It seems that setting the thermal limit actually only changes the temperature at which the big cluster is shut off. It doesn't affect the frequency curve AT ALL. I made some tests in which I raised the thermal limit after the big cluster was throttled down, and it did not increase its frequency again. It's hard to take a screenshot of this, though. The only temperature trepn can monitor is core CPU temp. However, another temperature is responsible for thermal management.

The thermal management of the big cluster looks someting like this:

if Temp below *whatever* use burst to the maximum
else go offline (or be forced to idle while grilling the phone)

This means a big cluster being forcefully kept alive by a high thermal limit does nothing except for drawing lots of power and raising the temperature.

update: under heavy load the big cluster does indeed throttle it's clock to something inbetween 1.84-0.63GHz shortly before it goes into idle mode (or offline, depending on the t limit)

The only time a big core @ 0.63GHz is utilized, is when the small core is at or below 0.96GHz. But only if the temperature is not too high (not sure how high, cannot measure this with sufficient accuracy). So @ 0.63GHz the big cluster is useless and should go offline.

The best temperature for sustained performance is 44°C. This ensures that the big cluster is used to its full potential as long as possible, while also making sure it is taken offline when it is no longer being used.

update: under medium load (e.g. browsing for some time), the big cluster will still sit unused at 0.63GHz for considerable amounts of time. To prevent this, a thermal limit of 42°C is needed. However, if the phone is sufficiently cool, a limit as low as this will take the big cluster offline even though it could still be used for some time. It's a tradeoff, I still recommend 44°C, though.

detailed and older tests below:

I ran some quick tests to see how the throttling temp limit affects performance. Tests were run on PureNexus 05/06/16 and Elemental 1.14 with GhostPepper profile. I used "Trepn Profiler" to record the data.

Instead of running a benchmark, I chose the more realistic ultimate stress test*:

*Update: As it turns out, Navigon is a really badly optimized app. Zooming the map while using GPS generates more heat than CPU benchmarks. So this test is actually a stress test.

entered a distant destination into Navigon (GPS) update: just zooming the map is enough, no need to set a destination

streamed internet radio with Xiialive and using its equalizer (Wi-Fi used for data, LTE active)

zoomed in and out on the map for about 6 minutes

It's unlikely that anyone zooms in and out of the map (update: see above, don't do this. It's the ultimate thermal stress test!) like a madman as I did, but the ambient temperature was only 24°C. So I believe at 30+°C this could actually happen while navigating, even without the constant zooming.

The first image shows the data for a limit of 46°C.

The big cluster (CPU6) is shut off at about the minute mark. After around three minutes, the small cluster (CPU1) throttles down to 960MHz and stays at this frequency. The zooming felt significantly more sluggish, but everything still worked. Just a bit slower.

The core temperature settled at just around 60°C.

Now at a limit of 55°C things start to get interesting.

At this limit the big cluster (CPU6) is never shut down and always runs at 630MHz. After two minutes the core temperature reached 73°C, causing the small cluster (CPU1) to occasionally drop down to 500MHz!

Whenever the frequency of the small cluster dropped that low, the screen and sound froze for a few seconds. The phone was almost unusable. Every touch needed a few seconds to cause a reaction.

Update: The idling big cluster tampers with the CPU load since it is the average load. CPU load on the small cluster is not lower.

tl;dr

Do NOT set the throttling limit above 46°C! It will actually decrease performance.

Update: 44°C is the optimum