I think it is impossible to get all of those components for $600.
well with my dell i have currently i have a pcu and ram and a fan i bought the case, power, gfx card, and motherboard for 600$ so i guess its a total worth of more than 600 which i should have specified
For gaming, get an i5-2400, 3450 or 2500K/3570K (if you want to overclock). I assume you're doing a gaming PC anyway, as thats what most people come here for. Theres no advantage to an i7 over an i5 for gaming. None at all.
Also, I assume if you're using 12GB of RAM that you're running 3 modules. Thats actually counter-productive to performance for 2 reasons.
1. Running 2 DIMMs or 4 DIMMs allows the computer to run in "dual channel mode". But running an odd number of DIMMs makes the computer revert to "single channel mode". (There is no tri-channel support on any modern CPU from either Intel or AMD- with exception to server-grade platforms)
2. You will never use more than 8GB, honestly, you probably won't even use all of 8GB unless you're doing heavily productivity work like Professional Computer Aided Drafting or something along those lines. That money for the 4GB extra RAM can be used to order a pizza to celebrate a job well done when the computer is built. You'll get more bang for your buck.
For a single 7870, you'd be fine with a Corsair TX 650 v2. Only get the 750 v2 if you plan on running dual 7870s at a later date, even then you could probably squeak by with the 650 v2.
A word of caution about the hard drive. If its an older hard drive, like SATA 1, you might want to consider getting a newer drive for the main boot drive. Also understand that if you are planning on using the hard drive because it already has Windows on it, it won't work. You'll need a clean, unbound copy of Windows7/Vista whatever the case may be. Expect that to add $100 to your cost.