These are my current specs:

Windows 7 home premium 64 bit
CPU; i7 990x extreme
Graphics; nvidia gtx 580
memory: 6gb
motherboard: ASUSTeK Computer INC., Rampage III Extreme.

If I will be able to, what other options should I change to have a smooth game?
I know auto detect is available but sometimes these aren't the best, and I tend to find myself changing this or that.

Possibly at around 30FPS, but honestly when I turn it on I can't tell a difference. You'd be sacrificing a lot of performance for such a subtle difference.

Oh I see, but the game should be smooth in all conditions and areas if I run it or should I be tweaking other options?

Just try it and look for yourself how it works.
I only have a GTX 470 and play it with >40fps, with only ubersampling disabled. So it might work fine on your system.
As james pointed out i also think ubersampling is the last thing you should enable.

Edit: Comparison and talk about ubersampling: http://forums.steampowered.com/forums/showthread.php?t=1896083

Agree subtle difference

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It's really not worth the loss in fps. Forget about it and max everything else

Yeah, just use the preset Uber, go into advanced options turn off Ubersampling and you'll probably get around 70+ FPS. Enjoy. :)

Ubersampling is very bad choice to improve the graphics , easy to the developer but bad for the perfomance and the final consumer . Really is the old supersampling .

They can be use another features with less perfomance drop to improve the game , like POM , realtime volumetric sun shafts - the rays of the game are a good solution to the preserve perfomance and look nice, but can be improve because really are not volumetric - Even a DX11 render with tesselation to the models . The perfomance hit with Ubersampling is 70 % and the only improve is a bit better antialeasing , in a game with that have a good antialeasing with MLAA . Even they can be improve the textures , because Ubersampling need a lot of space in the VRAM .

Sumary .. turn off Ubersampling !! And sorry for me engrish

If you have ubersampling on and can't tell a difference then I'm afraid you either need to play at a higher resolution or you aren't looking hard enough.

Edges are super soft, the fidelity is really nice.

I would like to have it on, but ubersampling at a decent framerate (close to 60fps) is way out of reach of most users right now and as good as it looks doesn't justify the fps hit.

Sorry but you shouldn't need to look hard to see a difference. When you need to stare and squint at the screen then you know it's a feature you can really turn off and forget about...

I'm not saying you have to look hard. I don't have to look hard, and I'm nearsighted.

Like a lot of screenshots on TW2, it looks great when you see it in motion, and it's easy to notice what it does.

but for most people ubersampling is either extremely low like 10fps or even 20fps so it doesn't justify the fps hit.

Plus at that low fps it's hard to see the gains because everything is so jittery

I have a 2600K at 4.3 and a GTX580 at 1920 by 1200 and ubersampling is unplayable. 12 to 30 and jerky. I get 45 to 70 average on ultra without ubersampling. So far no one can run it smoothly. Maybe with new drivers for SLI and Crossfire but not now..