OC-ing your CPU can get awesome results, but not if you want to use stock cooler.
an aftermarket cooler must be there to support the heat coming off the CPU when been OC'ed.
and you have a decent budget, IMO.
and you want to have three things, if you want to OC, and also GPU (may be 4, if you want one more ram stick too)
1. OC-able Mobo LGA 1155
2. Aftermarket cooler + additional fans for cooler/case fans (if you dont have enough)
3. a GPU
4. 4 GB Ram stick (same config as the one you have)(optional)
Budget = 25 k
Topgear recently suggested me that CM hyper 212 EVO (one fan included) is one of the best VFM aftermarket coolers also good for OC
we may go for two more fans, one for the cooler (so the cooler now has 2 fans) , and one, you put in the cabby.
CM Hyper 212 EVO = 2.1 K
2x120mm Fans = somebody suggest exact models) (1K ,AFAIK)
1x4 GB Ram = 1.6- ~2.3 k (dunno ,since OP hasn't mentioned the model of the one he has already.)
MOBO = ASUS P8H77-M = 7.4 k
total (with RAM) = 12.1 ~ 12.8 K (leaves 12.9 ~ 12.2 K for GPU)
Total (without RAM) = 10.5 K (leaves 24.5 K for GPU)
somebody suggest a good GPU too, since i have no info about good GPU's
also one thing must be considered , whether the current PSu can support the additional components bought (yes, the GPU specially.
)
if the PSU is also to be updated, get the intel mobo instead , and you have 3 k more for the PSU + GPU
: Refer to the Manufacturer's website for full and correct Specs, except, ofcourse Sammy products : 
