I think I did a pretty darn good job. You can see the reflection of my iPhone camera in the last picture.
Nice! I've never seen a soldered die this clean! Did you use any polishing cream/pad, or just conductonaut?
I ordered a copper IHS which is due to arrive on Wednesday. I want to do everything possible to keep this thing as cool as possible.
Yes, with LM+IHS, you should get a 10-15℃ drop, compared to stock. I assume it's the Rockit Copper IHS. If yes, then note that since it's not nickel plated (and its surface, although very flat, not mirror polished), the gallium in the LM (conductonaut is a type of galinstan alloy) will slowly diffuse into the copper to form a copper-gallium alloy (resulting in increased temps), so you might need to replenish/reapply LM for a second time after a few weeks. After that, the diffusion becomes slower.
As tempted as I am to install this thing, I don't want to have to redo it all again in 2 days, so no testing yet. I'll be updating this post with more details when the copper IHS arrives.
In the meantime, (if you still have your 8700K) you could try testing with Prime95 (if you haven't already) to make sure that your M/B can handle the extra load. Using Prime95 v26.6 (i.e. non AVX), run a torture test, for at least 30 minutes, with the settings in the attachment. It would draw ~180W of package power, so about the same (if not a bit less) with what an overclocked 9900K would draw under real-world heavy workloads (e.g. handbrake, blender).
If, during the test, the clocks remain stable at 5Ghz (you could check with Intel's power gadget), then you should be good to go, otherwise, you might also need to look into improving your VRM cooling while you are at it.
Good luck and have fun!