Frame Rate Lag on New Mission Load

I'm noticing an issue with the frame rate being low when mission is first loaded, as if the CPU is still busy processing something when your player first appears when you start up the first mission, but then after about 5 to 10 seconds (longer if your mission has a lot of objects), the frame rate jumps to a much higher level, as if whatever processing was being done as a result of some kind of initialization, is now done and CPU freed up to improve frame rate. Or perhaps its the video card being tied up.

For example, here's the 1.5.2. Stronghold level first booted up. Framerate at 20.

And here it is about five seconds later - jumps to framerate of 61 all of a sudden

The framerate difference and time it takes for the higher framerate to kick in is much more extreme on missions with more objects.

Also, one more thing to note in this mystery, I have three computers and it doesn't do this on the older computer running at a slower speed with an ATI 9200 card in it (laptop). But it does it on both my desktop and my new laptop both of which have nvidia cards and both of which have dual core processors. So it would seem to be an issue with perhaps nvidiea cards or dual processor machines?

Any insights, hints, clues, etc. would be greatly appreciated...

Thanks!

Peter