i play all the total war series games, and atm waiting for rome2 to come out,
for most of the series in very large battles and high not ultra settings in dx11 it will max out a i5 cpu and drop down to 30/60fps with a good card medium to high spec video card.
you have to play with the settings on a i7 and top end gpu to get it above 60fps in massive battles with everything on ultra in dx11, it's how the game has been written, not the cpu or gpu fault etc, some mods out that will make the games look as nice without loosing anything but speed it up some tbh
darthmod is one of them, but there are many others
i found the i7 better for total war than an i5, but made no difference for most of my other games like farcry, bf3 , skyrim etc
never played dayZ or online either as old and don't like multi stuff, single player only for me