Thanks for your hints, but unfurtunately I am still in trouble here:
The game again becomes so slow that it is practically not playable any more
I have now tried a few things:
1.) rocks2rockets - using rocks2rockets instead of cavemen2cosmos (I have not tried c2c with the options 2 and 3)
it was working well at the start but it is getting extremely slow now in the ancient era on a small map
2.) viewports are on now. It does not seem to help fight the slowness. It just creates some graphics strange effects, which seems to be a known side effect of the viewports.
3.) tried the 3GB switch. Civ refuses to start with it
a.) adding /userva=2900 or other number did not help
b.) adding physical memory - had 2 gb physical memory plus 2 pagefile before, now have 3gb physical memory plus 2gb pagefile
the error message is
http://forums.civfanatics.com/showthread.php?t=133003 (is there any solution in this thread, I spent some time reading it, but it is very long)
but I only get it with the 3gb switch on
I did not find a solution for this problem yet.