Cool. 12GB is kind of a weird number. Do you have 1 stick of 8 and 1 stick of 4? Or do you have 4GB built into the motherboard and 2 sticks of 4?
Or does it actually have more than 2 slots?
just did that myself (install 12gb ram). i had 2x2gb/Gskill Ripjaws sticks of ddr3 layin around (from an older setup) that i wasn't using, and decided to give it a go. i never bothered to install it before because i didn't want to screw around with my overclock settings and 8gb seemed to be doing fine ...so i left it as it was.
i have 4 ram slots on the motherboard ...2 banks ...so i installed the 4gb in the unused bank and cleaned out all the dust off my cpu heatsink (noctua nh-d14) ...there's wasn't that much dust, but a little build up (i typically clean out my pc of dust with an air can every month or two, so there wasn't a lot of dust ...but it was still good to get at the harder to reach spots). had to remove the cpu heatsink to get at the ram slots ...which was alright since i was due for some fresh thermal paste on the cpu.
put it back together and of course the previous overclock was a little unstable ...but might have been due to the ram voltage being set to the low voltage of my other ram (2x4gb Gskill Sniper v1.25). the 2x2gb Ripjaws was listed for 1.5 volts ...so anyway, i set it to 1.5volts and 9-9-9-24 timings @ 1600mhz, bclk@ 200 x 19 for 3.8ghz. i also up'd the cpu voltage to 1.3 volts ...up from a previous of 1.26v, to make sure it was getting a decent amount. i then ran IntelBurnTest for 5 runs @ max memory and it passed ...ran it on two occasions @ 5 runs/max memory (takes almost 1 hour at almost constant 100% cpu load), and it passed both times, so i think it's probably stable. seems good ...its not acting strange or anything. the hottest the cpu got during the burn tests was 61°c or 62°c at max load ...(which is about as high/hot as it ever got) so it's staying cool and roughly the same.
also verified that the ram is working in dual channel mode via CPUz ...everything seems good.
so yeah, it was a small upgrade from 8gb to 12gb, but i had it laying around ...so what the heck ...12 is better than eight.
haven't really upgraded this pc in a long time ...like 5 years maybe? can't remember ...but the main specs are :
intel i5 760 @ 3.8ghz
asus P7P55D-E PRO motherboard
12gb ram
msi twin frozr gtx680 4gig
1.5tb hdd
asus 24" monitor 1080p
still runs the games pretty good, so i never bothered to upgrade ...ie, Battlefield 1 @ 1080p is almost always 60fps using the Ultra graphic settings (during the single player campaign ...haven't tried multiplayer yet, since i just bought the game over the holidays).