What is your monitor situation and the rest of your system?
Generally, I recommend a single GPU, unless you want performance beyond what a single card can give. Crossfire and SLI have come a long way over the years. The majority of games work with it well, but not all do. Nvidia, however, has a little better track record.
yeah... my monitor is a single 1920-1080 and yeah im not sure I feel like a single 7970 would be sufficiant and also do you know if it runs in 3 times cf? or just 2?
If you that monitor is the typical 60hz monitor, a single 7970 will be enough to max most games, except for the most demanding, which it still will come close. The 7970 and 7950 allow for up to 4 way crossfire, but the 7870 and below only allow 2 way crossfire.
I agree about going 1 gpu vs 2 or more. sli/crossfire is not supported in some games, and you may encounter micro stuttering which would negate any
measured increase in frame rate. Get a hd7970(non ghz ed.) with custom cooling and overclock it yourself. You'll get a higher overclock going that route
than if you try the same on a ghz ed. card. A single "normal" 7970 will run most games pretty well at over 3 times your res, and you can push it a lot
harder when you overclock. That should last you at your res for quite a while.
A quick reminder about 7970 clocks and 28nm silicon. 7970 defaults to 925 core, 1375 vram(5500 gddr5). 7970ghz ed. defaults to 1000 core, 1500 vram
(6000 gddr5). However, the voltage is bumped up pretty aggressively on the 7970ghz ed. to ensure stability(perhaps more so than is really required). A
non ghz ed. 7970 should overclock to 1200 or higher on the core(best done with a custom cooler versus the reference amd style cooler to keep temps and
noise better in check). If you don't overclock, you are potentially leaving a ton of performance on the table. It's free. Take it.(all values are in mhz).
I forgot about boost(1050). Not sure how often 7970ghz ed. runs at that speed(may run into tdp throttling in some games that will limit it to 1000).
A good tool to help with overclocking endeavors is MSI Afterburner. A popular program many use to test the stability of their gpu overclocks is Furmark.
If you reach a stable overclock using Furmark, you should be more than fine in games since Furmark requires a lot more power than games do.