During mid game my performance always tumbles and turns taking up to 1 or 2 minutes is common.

I also noticed taking ships from fleets or adding them take 7 or 8 seconds on my AMD X2 at 2600 Mhz while my
notebook with Pentium at 2Ghz did it in less then a second.

Finally discovered that the virus scanner i use slows down the game a lot when lots of ships are moving about
and since i excluded the Galciv2 directory from the realtime proctection turns take between 5-20 seconds again
and game performes is a lot faster.

Also loading saved games takes a lot less time now. Overall i am happy this issue is solved for me