Possible FPS help with Demo 2. Maybe FSX also?

I do not have FSX yet. Been reading about all the FPS problems. I was messing around with the Demo 2 of FSX last night and decided to import the Piper Cub from FS9. Easy to do and it worked great, to my surprise. I had my scenery sliders set very high and was getting FPS around 5 to 6. Then, I started messing around with the ALT and Enter keys to window the FSX Demo 2. Amazingly, my FPS jumped into the 40s. It seemed like a sort of joke, and I just thought I would buy FSX and run it in the framed window. After flying around a while longer in the Cub, I used the ALT and Enter keys again to unframe the window and the frame rates remained the same, in the 30s to 40s. I looked into the FSX Demo CFG file and saw that there had been changes done to it but don't really understand what they were all about. I shut down the FSX Demo 2 sim and started it all back over again. The frame rates were down at 5 to 6 again. I selected the Cub and they remained low. I selected Alt and Enter a couple of times and nothing changed. Then, for reasons unknown to me, I selected Alt and Enter and the thing went back to running smootly with rates in the 30s to 40s depending on what I had my nose pointed at. I could select all the other aircraft in the Demo and the FPS remained high. I have no idea why this is happening. I only can report to you what I saw and am now seeing with the FSX Demo 2. I'll give you some of my system stats and FSX Demo 2 settings, but I consider them irrelevant to this post, as what is significant is that I received such a terrific jump in FPS by windowing back and forth with the ALT and Enter keys. System is an AMD 3500/1 Gig Ram/GeForce7800 GT OC PCI ExpressSettings in FSX Demo 2 were all in the middle of the sliders on the left side of the Scenery Tab and completely maxxed out for Scenery Complexity and Autogen on the right side of the Scenery Tab. The traffic stuff was all around 25% and I was not using any weather stuff. Previous to doing all of this, I had never had FPS over 15 with the Demo seemingly no matter what I did. My system gets around 40 plus FPS with the stock aircraft in FS9 with all sliders maxxed out depending on location. Around 25 in Seattle. I find this all really goofy, and offer no explanation whatsoever for it. Your mileage will probably vary. This is simply reported to offer some possible help for those of you with FSX. Were I reading this and having problems with FSX, I would give it a try. I hope it helps in some possible but unexplainable way. Take care,RazorbackRogers, Arkansas