For gaming, the ONLY ivy bridge cpu that can be overclocked is the 3570K.
The 3770K is $100 more, but the extra hyperthreads are largely useless for gamers.
Any Z77 motherboard will allow you to overclock a "K" to normal conservative levels.The higher priced enthusiast motherboards are for those who want to push their chips to dangerous levels.
As to sli, let me give you my canned rant on the subject:
a) How good do you really need to be?
A single GTX560 or 6870 can give you great performance at 1920 x 1200 in most games.
A single GTX560ti or 6950 will give you excellent performance at 1920 x 1200 in most games.
Even 2560 x 1600 will be good with lowered detail.
A single 7970 or GTX680 is about as good as it gets.
Only if you are looking at triple monitor gaming, then sli/cf will be needed.
Even that is now changing with triple monitor support on top end cards.
b) The costs for a single card are lower.
You require a less expensive motherboard; no need for sli/cf or multiple pci-e slots.
Even a ITX motherboard will do.
Your psu costs are less.
A GTX560ti needs a 450w psu, even a GTX580 only needs a 600w psu.
When you add another card to the mix, plan on adding 150-200w to your psu requirements.
A single more modern 28nm card like a 7970 or GTX680 needs only 550W.
Case cooling becomes more of an issue with dual cards.
That means a more expensive case with more and stronger fans.
You will also look at more noise.
d) dual card support is dependent on the driver. Not all games can benefit from dual cards.
e) cf/sli up front reduces your option to get another card for an upgrade. Not that I suggest you plan for that.
It will often be the case that replacing your current card with a newer gen card will offer a better upgrade path.