Yeah,the 670 is great value,performance is real close to a 680,for cheaper. The only thing better would be a HD 7970 ghz edition on sale.
Yes,just for gaming,you'll have alot of unused cores with an i7. However,if you're SERIOUS about graphic work,investing in an i7 makes sense.
You can save cash on the hard disk,disk drive and ram if it's ddr3.
You also want a z77 board,or it's variants H77 and B75,depending on your needs.