When I was putting my rig together, I went with i5-3570k because it is much more cost effective, and the i7 is not such an improvement, unless you are doing something really computationally intensive like folding proteins.

i5-3570k

You say you scavange other computers parts and could you name those? Just curious because as a computer, like most things, is only as good as the needed weakest link.

then not i7 and no K version for you.

like many other people said, take i5 and only regular variant, not k since it's made for overclocking. Also, when Intel finaly launches haswell prices of older chips may go down

i preffer 3570k

they will

In September.

I agree, most likely september or even oct-nov. Last time I was on a partner conference plans were q4 2013

An I5 3570 would be a cost-effective CPU in your case, but will be bottlenecked by the Geforce 650. Save the 110 $ difference between a 3570 and a 3770k and keep them to change your GPU at a later stage

You have money? Get an i7. Not so much money? Get an i5. Oh, and get a Blu-ray driver, too.

nvm

Why should he get a BRD?

No real reason to buy an i7 unless you simply have money to burn. The speed difference between the i5 and i7 is marginal. The main difference is that the i7 can provide 8 cores (4 physical ones and 4 virtual ones), whereas the i5 can "only" provide the 4 physical ones. However, most games don't even use 4 cores, so the i7 provides capacity that will only be used very, very rarely. For that, the price increase is way to steep.

Very few games are limited by the CPU. For most games, even an i3 is sufficient. As others said, it's mostly the graphics card that limits the performance, though even there, "limiting" might not be the best term. Most games are still targeted for 7 year old console hardware, and as a result, you can max out the visuals for most games even with an i5 and a halfway decent graphics card, and still get good FPS.

Why should he not?

Well guys & gals. It's official. I'm getting the i5-3570K. Now next is finding a suitable motherboard for it.

Some suggestions:

Z77 chipset unless you need to economize.

Top of the line:
ASUS Sabertooth Z77
ASUS P8Z77V Pro

Other good choices:
MSI Z77A-GD65 (I like MSI; I'd probably pick this one.)
Gigabyte GA-Z77X-UD5H