Question for "Windowed-Mode" users

After tweaking my sim setting to the best that I think they are going to get, and being a GeFrce FX 5200 Ultra owner, I settled for using windowed mode as I generally got better performance and didn't lose my 2-d panels (although I lose the 2xAA by using windowed mode). I have always waited until FS2004 starts and then "maximized" the window and can average 10-13 fps at the Seattle Tacoma default with the "Major Thunderstorm" theme. Tonight however, I didn't bother to maximize the window and lo and behold I am now getting close to 20fps during the exact same setting....Is this common knowledge that I didn't know about, or did I stumble into something here? If this IS common knowledge, do the majority of you use windowed mode in "normal" size, or "maximized"? Thanks from a very happy FS9 user.