The difference between the gtx 760 and 770 can only really be seen with the really graphically intense games. For instance, in Battlefield 4, the gtx 760 would run at high settings and the gtx 770 would run at ultra settings. I personally have a gtx 760 and it does everything I need but many people care about getting the max settings (which I don't care so much about as long as it looks good and is playable). But, the gtx 770 would last longer at higher settings in the future. Both are great cards.
As for overclocking, with the current generation of cpus, I don't see overclocking as being a necessity but more of a hobby/tinkering thing. If you are trying to keep the budget down, go for the no-OC build since you will save $30-50 on the cpu and another $30 on the motherboard.
If you needed the price of the OS in the $1000 budget then you could drop the SSD (gives no advantage in gaming other than loading times, but makes windows and various apps load faster) or you could drop the gtx 770 to a gtx 760 and fit it all in.