That is actually quite a bit more than my system. Although I'm using a Sabertooth mobo with 8 gig DDR3, SSD primary and a Radeon 290 from Sapphire, with a Corsair watercooler (that has an obnoxiously loud fan that is being replaced as soon as it gets here)
With that, I can run everything on ultra settings except for tessellation which I dropped to high and the last slider for additional anti-alias settings, as I leave it off. I can still manage 50ish frame rate and it seems smooth enough for me, as well as being stunning detail. (drop most settings to medium and 75-80 frames is easy enough) Mantle, I would run their benchmark and sometimes get a few frames faster, sometimes a few frames slower, didn't seem to make any rhyme or reason. However, on my 965 quadcore, I was getting 10 frames better on Mantle than I was on DirectX, which is pretty substantial.
I did reload all my drivers when I dropped in the 8350 and new vid card last night, so I may have negated some of the issues others were having, as I saw where someone mentioned a driver reload helped fix their problem. I will say it is night and day playing this game with a more robust CPU and graphics card, of course now I'm hoping Santa will hook me up with a 144Mhz 27" monitor for the holidays.
Yeah, the game works great in directx 11 mode, still hade flickering and tear, posted a video on this site on the flickering, got an answer, told me it was the cable from my gpu to my monitor that was faulty, I almost couldn't believe it, I mean a cable, lol. Still I changed my dvi cable for my newly bought displayport cable, and cover me surprised, not a single flicker. Flash or tear in the game, all that suit for a cable lol. I still wouldn't believe it, if I hadn't played the game for 4 hours straight today without a single problem.
The only other thing I did was a clean uninstall and reinstall of the beta drivers!

The game is great and quite good looking with everything cranked at max.
Still there is alot of bugs in it, minor and major once unfortunately!