Heart of Gold mission 2 - extreme fps fluctuations

I'm in the second Heart of Gold level, having discovered and activated half of the golden artifacts. However, after some time, after I created some outposts deep in enemy territory, I start getting extreme fps fluctuations, somewhere between 30 and 1 fps. The CPU load monitor in the Windows Task Manager is all over the place for my four cores. The game becomes completely unplayable.

I could repeat this behaviour by reloading a previous savegame and continuing to play. First my fps were at a steady 40 fps, then with the creation of outposts and expanding into enemy territory the same behaviour started to show - extreme lagging and fps fluctuations. Do you know of this issue? If not, can you please have a look into this savegame? Maybe you can tell where the issue is.

Best,

7

P.S.: I read through some of the bugtracker entries, and I can say that my AMD Phenom II X4 3.4 GHz normally runs WFTO with a steady 30-40 fps. Even the last mission of the main game ran flawlessly until the moment when I threw about 100 creatures on the enemy's defenses (then it became a slideshow). I have 8 GB of RAM (as menioned previously), and WFTO eats up to 6 GB of it (at times even more). Still, even then it runs flawlessly with all four CPU cores on full load. Only Heart of Gold mission 2 seems to be an issue (so far). I have yet to play the next mission.

P.P.S.: WFTO is the first game where I have to open my computer case and cool my CPU with an additional fan. Due to the load on all four cores the CPU heats up to 73 degrees Celsius and the BIOS warning starts beeping. With the additional fan I keep the temps around 63 degrees, which is perfectly fine.