Wierd crash, any thoughts?

Just to double check, you know that BCLK (Base clock) overclocking, overclocks Everything, right? CPU, PCI lines, RAM, Drives, Chipset... Everything! (Unless the board specifically allows separate CPU only BCLK overclocking.)

That's cool man.
But I would say, if you are still OC'ing solely via the base clock, or if you are doing it via base clock and multiplier at the same time without getting the multiplier solid and stable first, you are going to run into issues.
The base clock as said affects Everything even things within the motherboard and PC in general that you cannot see. The BCLK is there for Xeon and some X99 tweaking, it's never been a common thing in the consumer range (i5s and low i7s). Most consumer i5s/i7s will BSOD if you even look at the BCLK, even think of looking at it.
It's not used for the main OC because it affects so many things and is unstable and prone to issues, like passing a 24 stress test no problem, but crashing when watching a YouTube video, or causing "WHEA Event 17" errors.

You will also most likely be able to OC much further. You can always OC via the multiplier, get to your max OC, make sure you're 100% stable, then try tweaking the BCLK to increase it.

But it's obviously up to you, I'm just giving advice.

Yes, exactly right. Intel CPUs and the compatible motherboards are designed to be OC'ed via the multiplier. The multiplier is as it's name suggests, a multiplier of the BCLK. So if you set the multiplier to 10, that equates to: 10 x 100 BCLK = 1000MHz or 1GHz.

I would highly recommend you restore the default settings in the BIOS so you don't forget any voltages or settings you may have changed, then start with a fixed (Manual) VCore voltage of something like 1.25v or slightly higher, which *should be fine with your cooler. If you're concerned of temps, always start with lower voltages and work up. 1.30v is normally about the max safe voltage for a Hyper 212.

Once you have a fixed VCore of 1.25v-1.30v, then simply increase the multiplier from 40 (40 x 100 BCLK = 4000MHz/4GHz) to something like 45 (4.5GHz). Run AIDA64 or whichever stress test app you use, for at least one hour. If it passes with no issues, try bumping up to 46 (4.6GHz), and repeat the same hour test.
Eventually you will crash or blue screen, which tells you, either you need more voltage or lower the clock speed. If temps are fine, then try increasing the VCore slightly, very small increments like 1.300v to 1.310v, and rerun the test.

Remember that temps under stress test load will be 10-15c higher than normal load, they are designed to push way beyond what you will ever do with the PC. So if your temps hit 90c, that is high, but real world temps will be more like 70c-80c which is absolutely fine.

When you think you have your max overclock, run a stress test for a *Minimum* of 12 hours. Some times a PC can appear stable and pass even 8-10 hours... then suddenly crash. So the longer you test, the better.

Also, a very important thing that 95% of people forget or simply don't know about is, WHEA Events. This is where your OS (Windows 7/8/10) is unstable because of the OC. It can cause crashes, driver failures and poor performance. What that means is, your OC might seem perfectly stable and pass a stress test, but it's actually just slightly unstable at certain speeds and loads, so Windows starts experiencing errors.
WHEA Events (Code 17 and 18 if I remember correctly) can be viewed and checked in the Windows Event Viewer.

When everything is 100% stable, then you can try to OC a little more via the BCLK if you want.

One last thing. OC'ing memory makes very little difference and in many cases Zero difference in real world use. You would have to go from 1600MHz to 2600MHz to even notice a tiny difference, and even that would be almost unnoticeable. Closer or lower timings can make a little difference as they are Latency. Timing are the numbers on your memory like: 9,9,9,24 or whichever numbers your memory has.
For gaming, 1333MHz vs 3000MHz = Zero, nothing, Nada, nil.

Hope this helps