I do not have a thermometer, I did a quick test, sticking an old Xeon heatsink which I salvage from garage, it certainly drops the temperature quite a bit, the back of the AP is less hot to touch now, at least the rubberband did not deformed :lol:
I think I am heading the right path, next is to find a way to affix these and decide how and where to mount the AP 
Please do us all a favor and toss that heatsink. 
Your AP will be just fine!
Out of curiousity, I did a proof of concept on the Route 10, bam, I can see a significant drop on the temperature from 48.7C to 43.7C, this is with the Route 10 under minimum load (2 devices), previously I seen around 50C with AP6 attached, I am yet to attached the 2 x 10G ports with the SFP+ transceivers which are pending deliveries, it will surely much higher in temp, worse I am going to put the router in a enclose cabinet, so I am going to affix a heatsink onto the router as well, stay tune 
More order from Aliexpress, I am going to DIY a mounting bracket using the Aluminium plate, it will be hanging onto the exterior of the cabinet door, I hope the 1mm thickness can withstand the router weight, anything thicker will require specialize tool which I have no access to.
I’m enjoying your heatsink adventure stories!
Regarding the Route10, I recently installed mine in a narrow networking closet too, and my temperatures were a bit high. My Route10 is connected to 2 10GbE Marvel based SFP modules and it is connected to a switch, and 2 APs. Temperatures ranged from 44 to 50 celsius, which looked to operate beyond the recommended operating temperatures with 2 SFP modules installed. I did return my Marvel based SFP modules and swapped them out with the Broadcom based 10GbE modules and these take less power. Temperatures dropped about 4 celsius with just that change. I then added a USB powered fan controller to have a 2x140MM intake fan blowing air directly on the Route10 with a 2x140MM exhaust fan. Temperatures looks to be 36 celsius now.
Fans are silent (Artic P14 Max), but it doesn’t have the cool factor of a heatsink, haha! This worked for me if you wanted to consider something like this.
You really don’t need to add a heatsink lol. The shell is the heatsink, thats how it’s designed.
I found that the Route 10 runs a significantly cooler than my old UCG-MAX and Firewalla Gold Plus. Room ambient temp around 20c, R10 always <50C - usually more in the 38-43c range thats with 2 x SPF and 1GB wan , 2x1gb lan.
The unit sits on a Server Rack Vented Metal shelf which acts as a huge heat sink.
While finding another way to mount the AP, I open up the 6 screws of the AP and surprised to find out there is 0 heatsink in any of the chip, is that normal? Can anybody from Alta Labs confirm this is the design?
Moreover, there is 0 vent anywhere on the cover, I think that may explain the exceptional heat of my AP, I could certainly make some improvement with just a few DIY tweaks, but more Aliexpress I supposed, stay tune. 
My router cooling rack arrived today, another quick test, this time with the heatsink + USB fan turned on, the temperature drops further to 35.3C now.
I think this active passive combo is the way to go now as I don’t trust the fan can last long under 24x7
The back is where the chip that produces heat is hence why it’s metal on the back.
Extreme team
New stuff arrived today, so lets do the easy part, adding the heatsink to the route 10, it’s just a paste on as I tried to minimize the modification so that it’s reversible
The aluminium plate is a bit too long so I have to cut away a few rows of the fins so that it eventually sits right in the middle of the router
Here is the finished product,
The temp reading is at 44.7C now, not bad considering it’s running passive now with fan switch off, also it is not as impressive as the Xeon’s heatsink, I guess it’s because the fins are shorter but the aestatic is much better and it doesn’t look out of place on the rack
With USB fans on, it’s at 34.4C
The hard part is on the AP6, I still have not decided on the final design as I only have one shot on the 1mm alumimium plate, again I want to minimize the cutting so that the changes is reversible and hopefully I did not void the router warranty (but I guess I just did since I opened it up) :lol:
The excess fins that I cut from the route 10 is not wasted, I will use it on these two chips, but I need to further cut it to smaller piece and my metal saw could not handle such delicate task, I probably need to run some errant later to find a stronger metal cutter
Taa duh…the two long screws that came with the route 10 came in handy…it can actually go right through the screw thread…so I can use it to hold the aluminium block that I intend to affix on…this solves one problem and should provide very strong bonding between the router and the alumimium plate…stay tune for more
The most difficult decision next will be whether to open vents on the cover. I will be screwed if I made a mistake 
