Thanks for responding Leeghoofd. Apologies, but my internet has been offline and I just managed to get it working this morning again.
I had made the changes suggested by you - setting PWM Phase Control to Extreme as well as initially setting vCore LLC to Turbo. I also lowered my clock ratio to 40, kept the vCore at 1.35v and did a few IBT tests with 5 runs at maximum again. IBT testing passed at 4.0GHz, 4.2GHz, but failed at 4.4GHz with a BSOD and the CLOCK_WATCHDOG_TIMEOUT error
I then went back to the BIOS and set vCore LLC to extreme, as well as increasing the vCore to 1.4v. I set IBT with 5 runs on maximum and this time passed testing at 4.4GHz (image below)
At this point I admittedly thought that all was going well and decided to go for 4.5GHz, only to get another BSOD with the same settings which the 4.4GHz passed in the last IBT test.
What are the odds that my CPU is just simply incapable of doing 4.5GHz?