Use Shogun 2 Total War "Very High" settings,no AA, no SSAO, no HDR, no Soft Shadow and no Vigette.
[I guess] You might get FPS on campaign map around 30+ and battle map FPS around 30-40 when army march, zoomed out get decent smooth fps but zoomed in with soldiers are engagements is sometimes can slow down to 10-15 FPS but still playable and enjoyable. If FPS still worse, I recommend to reduce units detail down to "High" from "Ultra", might help boost FPS 4-5 FPS.
Comparison between "High" and "Ultra" units detail
-"high" will have less diversity than "Ultra" but still looks diversity individual person.
-"high" will have less animations "fighting" "death" "corpse" and over all animations than "Ultra" but still looks epic even on "high"
-"high" will shown less visual quality when zoom out, all units will more less details if zoom out far but still same quality when zoom in which is not make you feels loss quality in the game too much.
-"high" get more FPS!

and nearly same as "Ultra"
I hope you enjoy the game! Dustindesrctin, welcome to Shogun 2 Total War

I played Shogun 2 like 107 hours already and will be more like 200 hours in future
