Overclocking evga gtx670 help!

cpu: i7 3770k @ 4.5 turbo
cpu cooler: h100
psu: corsair hx750
ram: corsair 16gb @1600mhz
mobo:gigabyte ud3h-z77
gpu:evga gtx670 (standard edition)

I recently pre-ordered crysis 3 and want the best possible experience. Can you please help me overclock the gpu? Also I overclocked the cpu turbo to 4.5 and get around 78C on the hottest core after 20min stress test. Is that good or bad? Please give me all criticism, this is my first build.
-Thank you