ALL THESE RESULTS ARE FROM A 1080P RESOLUTION!!!!
The first GPU/CPU combo I used was...
AMD FX-8350 @ 4.3GHz (slightly OC'd)
R9 290 w/ 4GB
I was getting literally lackluster performance. On medium-high settings my FPS would hover around 40, then dip into the low 30's and even 20's during stack ups. Not even 20 x 20 fights, but really any unit fight where the unit size was large, or ultra. The Vampire Counts' tutorial battle was especially painful - with no shadows on, and mostly medium settings, moving the camera to the city walls would result in 20 FPS.
The second combo I used was...
AMD FX-8350 @ 4.4GHz (OC'd even more)
nVidia GTX 980 Ti
Slightly better but oh-my that bottleneck. I ran the game on mostly high settings, with AA, SSAO, reflections, and DoF disabled. Shadows on medium... I found that the ole' FX-8350 was holding back the 980 ti. I used MSI afterburner to check GPU vs CPU usage, and as you could guess - GPU usage never exceeded 60%, and CPU usage would fly between 70%-99%
Finally...
i7 6700k
nVidia GTX 980
After hours of replacing my MoBo, and CPU - I got my i7 build functional. ALL settings turned to ultra, EXCEPT shadows (at high), and AA is set to MLAA. SSAO is enabled, and unit size is ultra.
I pull easily 50-60FPS in non-siege battles, about 40-60FPS in sieges, and rarely 30-35FPS in ultra unit stack ups.
I'm stunned by how much a difference it made to replace my CPU and bump up to an i7. I used to think the 8350 was beefy sauce, but now I'll never look back.