So far it's all a bit inconclusive.
There were BSODs on 3/26 and on 4/6 that blamed a NVIDEA driver nvlddmkm.sys
Fault bucket X64_0x116_TdrBCR:D_Tdr:2_IMAGE_nvlddmkm.sys, type 0
Event Name: BlueScreen
Which seems to be a pretty recent one
nvlddmkm.sys Thu Apr 07 23:22:12 2011 (4D9E7F64)
You could try a rollback to the former version.
While the one on 4/13 is attributed to MEMORY MANAGEMENT
Fault bucket X64_0x1a_41790_nt!MiDeleteVirtualAddresses+3bdc0, type 0
. You said you ran Memtest lots of times. But did you test each strip separately? If not I would suggest to do that just to be sure. Right now you run without any detected virus protection while UAC is switched off. I understand why you do that but be very careful not to invite those nasties in and cause more harm since they have full admin rights right away. So I would for now run a full scan with Malwarebytes : Malwarebytes Anti-Malware is a free download that removes viruses and malware from your computer
Sorry I can't give you any better advice ATM