The normal frame rate for satisfactory operation of Extremes is 15-20 FPS. It is unlikely that you will see frame rates significantly higher than that any time soon.
The various features and improvements in Extremes, which is a completely different program from SS2008—and from any of the other games with which it is compared, tax to the limit the computational capabilities of most systems available to the majority of users.
It is the computations that must be done by the CPU before each frame can begin to be rendered by the graphics system that accounts for the low frame rates. Unless your graphics card is a very low-end one, it is unlikely that you would see much improvement with a more expensive one.
You may hear dissenting opinions on satisfactory frame rates from FSX users who have, apparently, not noticed that most airplanes move a lot faster than most ships; or if they have, are not able to see the connection between that fact and the necessity for higher frame rates in flight simulators.