FSX demo performance vs full game

[malibu43]

So, a while ago (on my old laptop, I think...) I tried the demo of FSX, and it didn't seem to run.

 

Well, today, I was able to run the FSX demo on my work laptop, and I was getting pretty good FPS up into some of the high graphics settings. I'm thinking now of giving it a try on my own laptop at home (I'll have to try the demo there, first). But, before I drop the whopping $15 for the deluxe version off of ebay, I was wondering if anyone knows of any reasons why the full version would not run as well as the demo. I was mostly flying around the islands with lots of water, so I could see getting slightly lower FPS if there were lots of trees and buildings around. I don't know though.

 

Any thoughts?

 

FWIW, I would consider 20fps just fine, and 15 in some situations acceptable.