Depending on which install and what mods I have, I get a regular 20 - 60 fps.
Vanilla SF2 I get 30+ just about all maxed out, mirrors on etc except horizon near (I keep horizon near on all my installs).
As long as your fps doesn't drop below the 20 mark things should look smooth anyway, in WOV over the Big H in campaign sometimes it'll drop to around 15 with all the SAM's, flak etc but still doesn't seem too bad.
It's horses for courses, some people will be happy enough at 15 fps others will moan at less than 30 (though I did read somewhere that you cannot really tell the difference between 25 and anything higher all things being equal - no stutter etc - but don't take me to task on that, maybe some people can).
I don't like to sacrifice eye candy if I can help it. Each to their own.