I have the suspicion the problems with booting (white screen with/without mouse) may not be limited (or even related?) to this motherboard.
I have a similar booting issue on my GA-z97x-UD3H, booting success seems completely random, but sometimes I get the "deadbeef" kernel panic instead of the white screen. Some have said the latter can be fixed by setting maxmem, but they also say it should not be necessary after installation.
I'm using iMac profil 14,1 at the moment (was using MacPro for Mavericks), and may be able to experiment a bit more tomorrow - will post if I find out more.
I did when I tried to update without the clean install. I had all sorts of missing mach_kernel and then boot 0 problems. I must have messed something up pretty bad because I had to repair the disk before I could create a new partition for the clean install. After that no more boot issues.