you will need to change the resolution to a wide screen aspect ratio but the fps should parallel. Its kinds like multiplying 2x4 and 8x1 and saying "which ones faster to do?"
I'm guessing, you're going from 1280 x 1024 to 1440 x 900. Actually that's lower than 1280 x 1024. So possibly a very slight increase in FPS, that you won't really notice.
It depends on the resolution you go to. 1280x1024 brings you about 1.31m and widescreen 1440x900 gives you less pixels with 1.29m. Very close so the difference will be minute and in this case you will get better. if you jump up another notch it scales pretty much the same way.
it may be 1680x1000 or whatever that one is...it will decrease frames if so. If you are going from 1280x1024 to 1440x900 there won't be much of a decrease at all.