I've been following this post and haven't seen any mention of load temps. While the RX360 system is awesome I wouldn't count on it making a huge difference with your issue/s. The Noctua is capable of 4.2GHz OC's in a lot of cases, and reaching a 4.0GHz OC shouldn't be any issue at all.
You should be posting screen shots or snips of CPUZ showing both the CPU and Memory tab so others can offer you more help with settings. Also post these screen shots showing Asus PC Probe where we can see voltages and temps.
Are you running the latest bios version?
The more settings you manually enter in bios and not leave on auto will only help in stability as well.
You may also find your CPU might do better by using a lower multiplier and higher Ref Clock which you mentioned you'd rather not do. With your mobo not having the VRM HS's I can understand this, maybe this is a sign that it needs to be considered as being replaced with a higher enthusiast board to give you more freedom to push the OC. If it was me, I would have chosen to get a better mobo instead of the RX360 at this point. By using the Ref Clock you'll gain more bandwidth and performance, it just takes a little more effort and really isn't that hard.
As others have already said it's pointless to just throw numbers at an OC, and even throwing more money (as in a WCing loop) into a setup isn't going to solve any problems until you determine what the real cause of the issues are.
Are you running Prime95 to stress test? I haven't seen any results of how it failed which is useful info to share.
Is your Ram (including the amount) listed on the mobo's QVL (qualified vendors list)?
Things like this will allow others to help you. Without good info from you we can't give good advice in return. I hope these suggestions will some how help you achieve your goal.
thanks for your help.