Maximum CPU temperature?

[Goosebump]

Apart from the thermal issues, everything seems to be working well, new thermal paste on order, I don't want to disturb things until it arrives  
(if it does make an improvement I will be having strong words with the suppliers!)

Rule #1 for applying thermal paste: A lot helps a lot

So this is wrong. May be in jest, I can't be sure.

You want to follow the less is more saying. If you have a big ol' fat smear of paste between the CPU and the cooler that's that much more thermal resistance your dealing with. A very thin layer of thermal paste is ideal. Using an old credit card is a good way to create a even thin layer of paste across the plate. There are youtube videos to show how to apply it.

In a possible appeal to authority fallacy: I've been putting together computers for over 25 years and nothing much has changed when it comes to keeping everything cool. Not "Cool dude cool" but cold, chilly, late fall weather in the higher latitudes, cooooool.

Everything about your temps suggest to me (and as others have mentioned) that the paste and by extension the connection between the cooler and the CPU is the problem. I would do the following.

1. Buy a paste removal kit and a tube of new paste.
2. Pull the cooler off, pop out the cpu and clean both plates with the paste removal stuff.
3. Wait a day and put everything back together with the new paste.
4. Wait 2 to 4 hours and then fire it up and see if the temps have changed. They should be much lower (30% or greater) than what your seeing even with the stock cooler.

Just my opinion. When it comes to building PCs there is almost as many opinions as their are components. But 9 times out of 10 temps that high aren't solved by case cooling because it's a cpu to cooler connection issue. AKA paste.