mixing ram on x58

i'm currently using 3x2gb Corsairs Dominator on triple channel on an Asus rampage II extreme. I was wondering if i could install another 3 sticks of OCZ XMP Ready Series, making my system 12gb. Is there a down side to putting extra memory on the non-triple channel slots and mixing corsairs with ocz. The timing is the same, both marked at 8-8-8-24. Also would i even notice an improvement on my system with 12gb ram.

if you are looking for 1600 ram speed you may have to get crazy on the vtt voltage. I have ran 6 sticks of 2 different rams without problems

The Rampage 2 can handle 12gb no problem. I ran 12gb of gskill PI Blacks ddr3-1600 all the way up 914mhz on 1.65 volts vtt was 1.43.