The Asus is great. I have the gtx 670 version. But be warned the 680 version is a triple slot cooler so it is a huge card. Make sure it won't cover a pcie slot you need on your board.
The gigabyte windforce is also an awesome card with an excellent cooler.
I wouldn't worry too much about factory overclocks. You can normally get any card to those speeds and beyond. There is no voltage control In these cards so you can oc them to their max with no worries of hurting the card.
As far as the 4gb goes you really only need that right now for triple monitor gaming. But that may change in the future. The only thing right now really maxing out the 2gb of ram on the normal 680s is heavily modded Skyrim.