Even for a 7970 CF situation (for 2 cards), an 850W PSU will be more than enough. I would get a Seasonic X 850 instead, unless you plan on getting 3 cards, in which case 1000W is reasonable. Instead of the Asus Sabertooth, I would get a Gigabyte 990fx UD3, UD5, or UD7. I prefer the all black design, and the price is very reasonable. Gigabyte makes great boards - I almost got one for my build, but I was drawn in by the Republic of Gamers Asus boards ;)
Unless you are sold on the Phantom, I would get a Fractal Design Define XL R2. I have a FD Define XL USB 3.0 (Titanium Grey), and I absolutely love it. Great quality for the price, and just killer looks. It's a bit cheaper, and it will offer just as much room for expansion and cooling as the Phantom. Fractal makes some great products.
If you want a better single card, get the 7970. If you get a 7950, though, along with all of the other changes, you would easily have enough money to fit a 120/128GB SSD into your budget. With a 7970, though, you will get more performance, naturally. I always go with the single strongest card I can get, but if you want to fit a larger SSD, such as a 256GB one, you may want to get a 7950.
Aside from that, you have thrown together a really good system. I would look into getting a nice mouse and mechanical keyboard, on top of everything else. I used cheap-o products for years, until earlier this year, when I bought a mechanical keyboard (Rosewill 9000 w/ Cherry MX Switches), and a nice mouse (Logitech g600 black). It changes so much! Using the computer becomes a lot more enjoyable. Sure, they are 'luxury' items, but you won't regret getting a nice set of peripherals :)