well you may have reached your window.
Again default everything in your bios. start with the basic oc. multiplier, and voltage. see if you can get the 4.6ghz to work after that. then apply your offsets, and what not's.
I found this litte guide, look it over.http://www.overclock.net/t/1291703/ivy-bridge-overclocking-guide-asus-motherboards
may find an answer.
...also have you updated your MB bios?