I have an interesting rig for this game in particular so I figured I'd do a gameplay video with the FRAPS counter turned on so I can help anyone with a similar setup... here are my specs:
PC specs:
Intel Core i7 920 @2.7GHz (stock speed)
Nvidia Geforce 660ti @ 1246Mhz turbo core clock & 3348MHz memory clock
6GB DDR3 RAM @1333MHz
Windows 7 Professional
The video:
https://www.youtube.com/watch?v=m_U79REUvkY
The game performs excellent in my opinion actually, considering the only recommended spec I have is the video card. This is actually maxed out with 2xMSAA on top, textures on High is the only thing I had to turn down. It's constantly at 30fps or above it (disregard the readings when it stutters) and if I lock the framerate it'll be even better, except for the occasional stutter that many people have reported even with the highest end rigs. In this video it stutters a little bit more because of the recording (and the PC bordering on maxing out the RAM) but you have my word that's it's smoother if I'm not recording anything. I honestly recorded more than a dozen videos but couldn't get it done stutter free (or at least like 90% stutter free). It does not stutter nearly as much when I'm not recording, Shadowplay doesn't have an impact on performance but RAM usage goes up a bit which in my case is enough to make it perform worse while recording.
I have 6GB of RAM and I need to clear up room by shutting down Chrome and other programs to get a good experience as well. Also, I recorded in 1080p, but I play on my trusty 22" 1680x1050 monitor, so I actually get better performance FPS wise than that, but I know most people use 1080p.
With more RAM, a different AA solution, either overclocking or a better processor, and with at least a video card equivalent to mine, you should be good to go at 1080p and nearly max settings except for AA. That's not bad at all, but the game has a myriad of problems and feels like it's not optimized in many areas despite the fact I consider my PC is performing above what I thought it could on this game.
If you need to push your graphics card a little further and need to overclock it, and you own either a 660ti, a 670 or a 680 (I don't know if other cards will work), try unlocking and modifying the card's BIOS to overclock it further than you ever could by normal means. My 660ti performs at a stock 670 level on 90% of either games and benchmarks. I have a full guide on how to do this, it's quick and easy and you can push your card further than you normally would with a stock Power Target:
https://www.youtube.com/watch?v=Cp0ZpkakAJ8 Edit: I don't take credit for any of this, I merely have a tutorial with the links so it's a good place for you to get it done quickly and trouble-free.
GPU info:
Bear in mind since I have unlocked and modified the BIOS, GPU-Z does not report the correct GPU and boost clocks.
Hope this post has been helpful!