DavidtheDuke posted this on Total War forum, worked for me.
"On a thread I found on reddit:
http://www.reddit.com/r/totalwar/com...ith_fps_drops/
"I had huge fps drops and this made the game playable for me.
Just change the affinity of the rome2.exe process in "task manager" to anything less than all processors press ok and then change it back. This removes the drops for me.
For some reason this seems to spread the load evenly among the cores for me where as previously one was used to 100% while others where hardly being utilized.
Hope this will help some others.
Edit: some further explaination provided by seriousdan: "Open your task manager with ctrl+shift+ESC, go to processes, right-click the rome2.exe process and click on "set affinity..."."
You can find other optional tweaks on their website
here. I did all of them but changed back to dx11, got everything running nice and smooth now. I also have my graphics similar to this guy on
YouTube which helps a lot.