Is this build good for gaming and somewhat cost efficient?

750w is abit overkill. 550w bronze should do.
A micro board in a full tower will look off.Get the ATX h77.
Otherwise good build.

A good build.
You have correctly budgeted more for the graphics card than the cpu.
For highest graphics, that is all important.

I have some comments.

On the cpu, the 3450 will do the job. If you live near a microcenter, they will sell you a 3570K for $190.
If you go with this, look for a Z77 based motherboard so you can overclock the "K".

8gb is good, but buy a 8gb kit composed of (2) 4gb sticks. That will give you dual channel operation.

Consider starting with a 120gb ssd and no hard drive to start with. 120gb will hold the os and half a dozen games.
If you use a 180gb or 240gb ssd, you may never need a hard drive at all. You can always add a hard drive later if you need to store large files like video's. A 60gb ssd is bare minimum for the os. More than you might like will be directed to it, and as it nears full, it will slow down. A larger unit will be better.

I like Intel and samsung better for reliability. Samsung is clearing out their 830 SSD's in anticipation of launching the 840 series.
You might find some good discounts.
Ingore ssd benchmarks. From a performance point of view, all the new ssd's will perform about the same as percieved by the normal desktop user.

If you love the case, buy it. But, it is larger than you need, and more expensive than you need.
You can buy a good quality Antec 100/200/300 series case for $50.
If you want the best M-ATX case out there, I can personally recommend the Silverstone TJ-08E.
It is very quiet with outstanding cooling.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

The psu is a good one, but the GTX670 only needs a 500w psu. A GTX680 only needs 550w.

Lastly, if you want maximum graphics, consider a GTX680. Yes, you get diminishing returns for the dollar, but the delta in price from a GTX670 has dropped. For $50 more(after rebate), you can buy a top of the line EVGA Superclocked, Signature 2:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

If you want to stick with a GTX670, I like this EVGA GTX670 FTW for a bit less. It has a higher boost clock and a direct exhaust cooler that sends the heat directly out the back of the case.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

OK so i upgraded my motherboard
link:
http://pcpartpicker.com/p/kYv8

^save on the psu and get your second stick of ram.