i've just read WAY too many reviews of all the various cards/models out there. and i have yet to see any single review show a worthwhile gain from an oc. in fact other than thermal throttling a reference card gets almost the same fps as a super ultra deluxe oc'ed and heavily cooled model!!
for instance the EVGA SC, which is a reference card, gets the same fps as the FTW+ card. $100 more and a ton of extra power used for around 1-2 fps gained. did not see any particular game that had some magical 25 fps gain or something. literally 1-2 fps was all any got.
this is due to the fact that boost 3.0 already overclocks the card as high as it can go anyway. so a manual oc only locks in a clock speed the card was probably hitting anyway. maybe an extra 50 mhz or so more that nets no in game increase.
have seen some watercooled cards that could hold the highest speeds for a lot longer and could get an extra 5 fps or so. well worth the extra $150 for watercooling the gpu
the old days of really significant gains are gone for now. rest well knowing that out of the box, the card is giving all it can with no help from you.