two 120 mm fans for high end gaming with OC

Every chip is different depending on voltages obstruction of airflow to many variables to give you a yes or no answer. You'd have to monitor temps and see if that is acceptable.

That's taking chances. I wouldn't do it unless you want to be running 2 Scythe Gentle Typhoons at 3000RPM and even then they won't be enough. What kind of case do you have and what make is it?

Viable... yes.

There is always a trade off between cooling and noise.

If both 120mm fans are either intakes(best) or exhaust you have a good start.
If one is intake, and the other exhaust, not so good.

Then, there is a huge variability possible in the cfm capacity of the fans. Higher rpm gives you more airflow, and more noise. You might also be able to opt for 38mm(vs. 25mm) fans which offer more cfm.

If you oc that 3770K modestly, there is not a lot of heat generated. Just keep the voltage on auto. That should give you an oc in the 4.3 range without the exponential heat buildup.
With dual 7970 cards, you do not need the added graphics power and heat that comes from overclocking.
If money is not a big issue, consider a single titan or GTX690 instead.
Lastly, a cpu or graphics card can tolerate high temperatures. They will downclock if necessary for protection.

What case are we talking about?

Since the brand and model of the case is unknown to me, I can't tell for certain how it would work.
It looks like there might be room for two 120mm intake fans in front. If so, I would move the rear exit fan to the front.

It also seems to me that the case is a bit pricey.
The antec 300 case, for example might be similar, and you can put two 120mm fans as intake in front.
I like front intake fans behind a washable air filter to keep the interior clean.
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129066

To my mind, a single graphics card is preferable, whenever it will do the job.
Here is my canned rant on dual cards:
-----------------------------Start of rant----------------------------------------------------
Dual graphics cards vs. a good single card.

a) How good do you really need to be?
A single GTX650/ti or 7770 can give you good performance at 1920 x 1200 in most games.

A single GTX660 or 7850 will give you excellent performance at 1920 x 1200 in most games.
Even 2560 x 1600 will be good with lowered detail.
A single gtx690 or Titan 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 GTX660 needs a 430w psu, even a GTX680 only needs a 550w psu.
When you add another card to the mix, plan on adding 150-200w to your psu requirements.

Even the strongest GTX690 only needs 620w.

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.

c) Dual cards do not always render their half of the display in sync, causing microstuttering. It is an annoying effect.
The benefit of higher benchmark fps can be offset, particularly with lower tier cards.
Read this: http://www.tomshardware.com/reviews/radeon-geforce-stutter-crossfire,2995.html

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.
The GTX780 and amd 8000 series are not that far off.
-------------------------------End of rant-----------------------------------------------------------

And... for gaming, save some money, and buy a 3570K instead. Few games can use more than 2-3 cores, so the extra hyperthreads of the 3770K are largely irrelevant.

That case is not a good one for air cooling. You can get by with a Noctua NH-D14 for cooling your CPU and grab a couple of Scythe Gentle Typhoon 1850 RPM Servo and you should be ok. It also looks like you can add fans to the side of the case next to the card, so I would do that. But when time comes and you are upgrading, you might want to get a high end case for your high end rig. Don't skimp on the case when you have quality parts that need enough air to cool them off and last longer.

I can see that you are in Austria, correct me if I am wrong. And your case doesn't even have a front fan, just 2 fan mounts on the side and a rear one. If you can afford it then do get a new case when you get those parts. I would not house those parts in the case that you linked.

You should be pleased with the NZXT 410 Phantom
Fans do not cool, they just move air.
The three fans that come with your case will do the job.

On a budget, I recommend an inexpensive tower type cooler with a 120mm fan.
It will cool better than the stock Intel cooler, be much quieter under load, and be easier to install.
Something like the cm hyper 212 or the Xigmatek.

A top end air cooler will cost 2-3x as much, and really is not needed for conservative overclocking.

Now that's a good case. I say fill the front intake fans and top exhaust fans. So put another 120mm in the front and add another 140mm up top and you will not need the side fan. That should be enough air in and out and your system should run cool. I am very happy for you bud. All the best!