I was working on a P8Z77 Pro board with 3770 not so long ago and ran into a similar issue - 2x 8GB (1600) sticks worked fine but more than that it hung. I did not get round to getting console output or dug too deep into the why but tried physical fixes first. I tried various permutations and found that (2x8) 16Gb at 1600 was the limit. I * think * (and dont quote me, it was a while ago) I managed to get 32Gb (4x8) working with 1333 sticks. I could be having a memory issue though (pun intended). I was going to try to use MRC instead of native raminit but got sidetracked and never figured it out - this page mentioned the MRC binary systemagent-r6.bin https://doc.coreboot.org/mainboard/asus/p8z77-m_pro.html