**Update on random crashes**
Before performing the stress test, I set the BIOS (VCORE, LLC as suggested)
I have since as recommended performed a stress test in Windows (bearing in mind my CPU is not overclocked or anything). Upon downloading and looking into it, I thought I would run a quick 5 minute test to see what would happen. After 4m58sec it froze and the fans fired up. I had a loom at the MOBO to see if there was any error codes and found it said C1. Gigabytes manual is not at all helpful at this point because it says the C1-9 is
'reserved' (not helpful).
Upon investigating this, suggestions were that it is RAM, well I had already taken this out and reseated it.
I did it once more, except I swapped their position in the slots (1-3 & 3-1).
Fired it up again and did a quick stress test and it sailed through. No problems, did a couple of bits, went back into MacOS, did some more bits with no issues... this was all since 10:30 this morning and I'm still here doing bits and it's running quietly, no dramas and behaving the way it should be.
Just finishing a couple of installs and getting things back to a place where I am happy and then I shall use SuperDuper to create a Bootable backup (just incase).
Thank you all for the help and suggestions, I'm not entirely out of the woods yet but I definitely feel that it is in a better place than it was a day or two ago!
Big shout out to
@CaseySJ @Ayvan @Higgie @hughythomas and anyone else who has contributed to helping me out, many thanks