You're missing a fair bit of parts there, but that's okay.
If you aren't going to overclock, the 7970 is worth it. That being said, I highly suggest you do three things:
1) Overclock. A mild overclock can make a big difference.
2) Going off of that, grab a CPU cooler - I recommend the Hyper 212 + or EVO.
3) Get an SSD. Even if you have a hard drive, get a 128GB ssd to put windows on - it makes a HUGE difference as to how fast and responsive your computer feels.