7950 is 356 bit like 7970 so you can crossfire it with 7970 in the future when they are cheaper because it's the same chipset. I use http://pcpartpicker.com/
to build my system. Try it out, I'm not sure if they will deliver to where you live but it's a good guide to build PCs because they will show you compatibility. See what you can put together and post the perma-link to your parts so people can comment and advise on improvements.
My build is:
7950 (960MHz stock, got it to 1010MHz without trying)
Asus ATX MOBO z77
Balistics 2x8GB ram @1600
1 Killa Watt PSU
I consider my system an overkill but I expect it to last for 5 years.
I have Photoshop, Sony Vegas, and play videos games open at the same time without a sweat.
The most Ram usage ive seen was 8gb once and processor only is at 100% when rendering HD videos.
I built it for under 1k USD about 6 months ago.