Oh man sorry to hear that, bad luck there . It really sucks losing a good chip I know how you feel!
You were playing with fire at those volts and cooling. Gigabyte boards set vcore a bit higher once you start going past 1.65, if you had a play with other boards in the past this jump would be familiar. It only happens around 1.65 in bios. This is normal. You really should have had subzero cooling for anything past 1.6 mate, I wouldnt stuff around next time no matter what board you use.
use stock VRM unless you specifically see an improvement. I very much doubt you will see anything change on standard cooling. It might make a difference with some CPUs subzero however. Always test extensively with stock on Gigabyte first though and then gradually work your way up that's my advice.