4.2ghz @ 1.35v is brilliant and hitting temps of 70oC, id blatantly try and push that chip beyond 4.2ghz, you have loads of headroom there, mine does 4.2ghz at 1.36v, gets upto about 70oC too, I don't have much time during the week to mess with testing etc, but come the weekend, i'll ramp the voltage upto 1.4v and see if she gives me anything extra.
I have the ram kit running at 3400mhz, 14-15-15-31-1T, Gear down disabled, power down disabled, I just left everything else on Auto, just left memtestx64 running all night, 7 hours no errors, got up in the morning and ran Google stress test for 2 hours, way tougher than any version of memtest, no errors, I don't really overclock ram either unless its a dead easy one to shoot for and 3400mhz was dead easy to get.
I then ran Prime95 26.6 blend which a lot of people will tell you is a waste of time, but Small FFT's just loop over and over every 2 hours, and don't touch the ram, the size fits easily into the CPU cache, blend on the other hand does one pass of Small FFTs staring at 8K passes, then a Large for RAM, then a Small for CPU, then a Large for RAM, so on and so forth, the longer you run it the bigger the problem size gets, ran it for 8 and a half hours on Saturday afternoon into Saturday evening whilst I was out, came home and it was still going.
2 days to get my system overclocked and stable exactly how I want it on an MSI X470 Gaming M7 AC, finished off with 8 hours of Realbench overnight, when I had the ASUS CH7 I was fighting for a week just to get the ram stable and it wouldn't get my CPU to 4.2ghz even at 1.425v, nearly threw the damn thing out the window, I was pulling my hair out with it, ASUS never again.