I have a fairly good processor (i5-3570k) so shouldn't be too bad right?
I run an i7-3820 which runs at a stock clock of 3.6Ghz - I had it running at an OC of 4.6Ghz for streaming, and I still couldn't mess with a 1080P res at a fast preset. It pretty much maxed out my CPU - then again, I was playing Hawken which is a FPS, so there's always fast motion scenes.
Your best bet is to stick with 720 if you want high quality, or at the very least run it at no more than 30 fps, then possibly run the "faster" encoding preset? I was streaming Hawken at 4.6Ghz (8 threads) on "fast", 3500kb/s with a 1280x720 resolution, and it looked impressive, but it used most of my CPU in conjunction with the game, however I did not lose frames for either.(I actually miss it, but I cooked some ram in doing so at the very least, so I stick to 4.3Ghz.)
My objective was to get a decent res, but a clean picture as well while maintaining 60fps. The game you linked to doesn't seem like smooth motion is characterized as being the most appealing aspect to the game, so you could probably get away with 30fps to cut CPU usage, 1080P with "very fast", as long as you can do the max upload comfortably, using 3500 kb/s for stream upload.
Hopefully you can use what I've typed as some sort of reference point.
