I actually happen to own a HD7950, paired with a Phenom II 1055T, and 8GB RAM. This card is an absolute monster and i have absolutely no regrets spending the extra dollars getting it, i paid 330USD for the Gigabyte version show here:
This has a Tri-Fan Windforce aftermarket cooler built right into it already so i would highly recmmend this, my case has a 200mm fan, and 4 120mm fans and this thing runs cool as hell under load, pardon my language. I get a steady 45C on games like borderlands, and it goes up to 60C on BF3 after playing for a 30mins or more, but thats the highest ive seen, and i play them ALL on Ultra-Maxed with 8xAA and 16xAA (Skyrim), ect
Edit: I did also want to mention that the 7870 has 256-bit Bandwidth port, while the 7950 has a 384-bit port, the Bandwidth gets a huge jump goign from 120GB/s to 240GB/s which is further future proofing the purchase. As a proud owner of one of these, it has NOT let me down! Good luck, man i hope this helped some!
I was actually going to get a HD 7950 but when I saw the 7870 drop to 220 I thought maybe I could just add 100$ onto the price of a 7950 and get a crossfire set up. This is why I wanted some info on whether the $100 I save is worth the performance i lose. I have seen some benchmarks and the hd 7950 does win by like 3-10 frames on most games.
EDIT: Also in Australia so Newegg isn't a viable option for me.
The biggest difference in the cards is the ram and memory bandwith. These two mainly become factors when you push to a high resolution past 1080p. If you plan on running 1x 1080p screen than a 7870 is a great choie. If you plan on going with a newer 2560x1440 screen, or an EyeFinity multi-monitor setup (5760x1080) than you definitely want to spring for the 7950. The extra gig of Vram and memory bandwith help at high resolutions. Outside of that, the 7870 should be able to overclock to near the 7950's stock levels, but at the same time, if you overclock a 7950, most can easily get past the ghz edition of the 7970's. My 7950 easily runs at 1100/1500 without breaking a sweat.