I built the x79 box in my signature this spring. I considered the 3820, but changed my mind after reading this review:
http://www.tomshardware.com/reviews/core-i7-3930k-3820-test-benchmark,3090.html
The summary is there isn't a lot of advantage to x79 if you're not going to do 6 or more cores. In my case, I choose to go up to the 3930k, but then computers are both my vocation and my avocation and I budget accordingly (I spend more than I can afford).
It appears to me you are overestimating the effect of cpu on your system relative to gpu. For gaming, a 3820 is more than you need and you can do a lot better than a 6950 for graphics. With any i5 or i7, watching video with as many browser tabs as you want open isn't even going to begin to stress the cpu. The extra cpu power is only useful if you're doing serious video or photo editing, some development and server tasks, distributed computing etc. I recommend stepping down to a i5 2500k or i7 2600k (I still prefer sandy bridge to ivy bridge by a slight margin because of the heat issues with ivy bridge) and spending the money you save on cpu and motherboard to upgrade your gpu. You should get at least a 7850, or better a 7870, 7950 or nVidia GTX 670 (or wait for the GTX 660 which is coming real soon). Take a look at these benchmarks of systems with a 7870 vs 6950:
http://www.tomshardware.com/reviews/radeon-hd-7870-review-benchmark,3148-6.html
The 6950 in BF3 at 2560x1440 struggles to get 12fps, while the 7870 gets 28fps.
In contrast, in the 3820 review you'll notice there is almost no difference in framerates between the i5 2500k, the 3820 and even the 3960x.
If you still decide to go with x79...let's talk motherboards. Picking a x79 motherboard is really hard (picking z77 looks even harder), but I think you picked the right one. If you want my reasoning read on:
ASUS is generally considered the premium mobo manufacturer. Its by a slim margin, but narrowing down to just ASUS left me with only 8 boards to choose from instead of 80+.
The last thing you want is a motherboard no one else has: the manufacturer is less likely to support it and you will have fewer online community resources. By this reasoning I narrowed the search to the RIVE, the Sabertooth, the Pro and the Deluxe.
The Sabertooth does not have the feature ASUS calls Q-Codes, which is a 2-digit LED boot status display. More than once in my career, I've only been able to get a build to boot by virtue of diagnosing these boot codes, so that eliminated the Sabertooth.
The Deluxe and the Pro are very similar, but I didn't need the built-in WiFi or second LAN controller of the Deluxe, which is more expensive, so that eliminated the Deluxe.
The RIVE has a bunch of specialized overclocking features that I don't need, but I was eventually won over by the wealth of activity on the overclock.net community about this motherboard:
http://www.overclock.net/t/1151946/official-asus-rog-rampage-iv-x79-owners-club
the RIVE is considerably more expensive than the Pro and really doesn't have any features most people (including me) are going to use. So I think the Pro is probably right for you (and probably right for me, but whatever).
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