More Fps in FullScreen mode

Hello everybody, today is my first post on avsim. Today i have an important question to ask you. I bought Steve awesome fix a few days ago. My experience with this new rendering is great But still there's a problem. I use two screens, a large one for fsx and an other one for charts and other stuff. So it's not possible for me to use fullscreen mode.The probleme is that i get less fps in windowed mode than in fullscreen mode and i can't find why. I got an Ati readon Hd 5770, an Ivybridge Cpu and Windows7.