Is this system ny good?

Never heard of your PSU . Better to stick to a recognized brand . Corsair , seasonic, antec , enermax , pc power and cooling .
You need 800 - 850 watts for GTX's in SLI

The 2500k is the gamer cpu . Hyperthreading wont help so the 2600k is pointless

Your SSD is too small . Windows and 2 games......... really?

Your motherboard only supports two graphics cards so trying to add a third is not just pointless from a performance stand point its also impossible without using a hammer and a casual disregard for all things electronic

I included the SSD ONLY for the windows!
I will be doing A Lot of multitasking, besides in the motherboards description, it says, that it supports quad sli!
Then what is the difference between the branded power supply?

I do not care what the description says. The model you specified has only 2 PCIe X16 slots. You can tell by looking at the pictures.

A quad SLI board will cost not less than about $300 because it needs some extra hardware not built into the chipset.

http://in.asus.com/Motherboards/Intel_Socket_1155/P8Z68...
What about this one?

No the P8Z68-v PRO will still only do 2 cards in SLI.

The cheapest board that supports more than a 2 card set-up, i think, is ASRock Extreme7 Gen3 which is priced about $270 http://www.newegg.com/Product/Product.aspx?Item=N82E168...

For more than 2 cards in SLI, the motherboard must have something called an NF200 chip.

http://www.asrock.com/mb/overview.us.asp?Model=Z68%20Ex...
What about this one?

Not a bad choice, but you would be better off with the GEN3 version (ASRock Extreme4 Gen3).

I think, it's Gen 3, but, Does it support 3-way SLI?

See my post above ^^

The board you linked me to wasn't the GEN3 version, it was the old standard Extreme4. The Extreme4 Gen3 version is black and gold colour scheme.

Link here for ASRock Socket 1155 boards: http://www.asrock.com/mb/index.asp?s=1155

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The cheapest board that supports more than a 2 card set-up, i think, is ASRock Extreme7 Gen3 which is priced about $270

For more than 2 cards in SLI, the motherboard must have something called an NF200 chip.

I have just watched a video review, from Newegg, and Paul said, that it can run tri sli!

" - ... If you're using 2 cards, they operate 8x, 8x. If you're using three cards it will run at 8x, 8x and 4x..."

Which motherboard?

ASRock Z68 Extreme4 Gen3

By all means wait for a second opinion, but I was fairly certain that board only supports 2 cards in SLI or 3 cards in crossfire. For 3 cards in SLI the NF200 chip was required.

As i said though, I might be wrong so await a second voice on here