fps depends how you will programm it and how many triangles you will have in world, also if you use special techniques like LOD system and others, you can maximize FPS.
also depends on graphic card…
everything depends on not just this but many things. like your programming skill, knowledge, triangle count, shader types, optimize libs and much more. Graphic can be reallly awesome and you still can have very good fps.
btw myself i see fps is not a problem. i already made world full of high triangle count trees and big terrain and i easly got 60 fps on my 3 years old graphic card.(average one for this times)