http://www.xtremesystems.org/forums/showthread.php?271749-Maximus-IV-Extreme-2600K....-Over-5.9-GHz&p=4889995&viewfull=1#post4889995
and sometimes max multi depends on bios version and cpu too. i had a 5.9GHz cpu that boot OS max at x57 on m4e with 1303bios, but with 1902bios x58 & x59 works too. and another 5.9GHz cpu works fine at all multis with both bioses