I got fed up yesterday at the server, I was looking at my memory usage indicator more often than my fuel gauges;
I would decide to enter or leave a dogfight based on my available RAM
So, I played around with the video settings.
With the settings below, the game starts with some 500Mb RAM less than my previous settings and the memory leak is considerably slower!
The only downturn is that I can not see the grass anymore so it looks a bit miserable during take off. But the trade off is worthwhile for the peace of mind

Mind you, land detail is still high so from above the view is still wonderful, albeit without trees

I am sure there is more margin for trial and error but this was already a major improvement at little sacrifice for me.
Here is a screenshot of my settings in case anybody becomes as desperate as I was yesterday...
~S~
PS. Thanks for the answer Bliss, and for the download zip - too late, I had already set my eyes on the pinups...aaarrgh!
I have to think of something; I do not use the steam account CoD, I have a separate version on a different directory (in order to avoid any mess-up with the RAMDISK I have set the game up at).
PS2. needless to say, I do not have the problem with the train (NV)