Looks good, you can get a 7970 + 3 games from Newegg for less than the 760. Will easily out perform the 760. Otherwise looks good. Can't speak for Thermaltake PSUs (never used one) though.
You have a pretty nice build there. The only gripes i really have are to do with the PSU and the RAM.
Try and keep your RAM at 1.5v stock if you don't want to deal with compatibility issues out of the box. The PSU is just overpriced for what you get. You can get better units for cheaper.
http://pcpartpicker.com/p/250kI
Here is what I could come up with. OpenCL is being adopted more and more into Adobe products, so the 280x is an admirable choice at a decent price.
The lower CAS latency on the RAM will help with any form of editing you wish to do.
The PSU is decent and inexpensive. Unfortunately if you plan on adding a second video card, you would have to go with a 700w PSU. If not, there's this.
Most of the time I would suggest getting a CPU cooler right off the bat and start overclocking, but if you're running a lower budget system for gaming, I would recommend getting a better GPU and grab a cooler later when you have the money. It's an easy and inexpensive future upgrade. Graphics cards, not so much.
I don't think I would get another video card for this build. But I was planning on over-clocking the CPU sometime in the future, i can always grab a corsair h60 or similar if I need to. So far I like your build better than mine.
R9 280X is an HD 7970 with a new sticker on it. Literally. Maybe a slight change in clock speed, but that's pretty much it. They even crossfire together.
For a CPU cooler, I would highly recommend Cooler Master's Hyper 212 EVO. The low end all in one liquid coolers can be outperformed by these cheap, budget air coolers.
I know we selected a 650Watt PSU, and I was reading the GPU specifications and found this::750W (or greater) power supply with one 150W 8-pin and one 75W 6-pin PCI Express power connector recommended::
PcPartPicker doesn't give any flags because the estimated wattage is 444.
should I be worried about what the 280x specifications said ?
650w is more than enough to power a build with the R9 280x or the 760. It also delivers p to 46A over the 12v rail, which is also more than enough to run these cards.
Nope, this has been tested everywhere. Pretty sure linus did a video where he was using a 6990 (2x6970s effectively) going through a single PCI-E 2.0 X8 slot and found the frame difference between that and 16x was within the margin of error. If high end cards don't fully saturate an 8x PCI-E 2.0 slot then having 3.0 is going to make no real world difference.
Build looks good. You don't NEED 650W, and a 550W PSU would work just fine. Keep the Asus motherboard, as it has better cooling and VRMs than the Gigabyte in Namix's build.