SilentCat: Hello!
I just recently found GoG and I am absolutely loving it.
Anyways, I just recently came across a strange issue with Earth 2150.
The game ran fine after install, no hitches or stuttering whatsoever. I installed Real Myst (Great game by the way!) and played through it, then returned to playing Earth 2150. The game now was stuttering and playing extremely slowly. With no obvious issue, I went into the task manager and unchecked one of the processor affinities to allow the game to only use one CPU, and sure enough the game is playing smooth as silk again.
Now, I'm going to guess that the little application that launches with GoG's games, 'gogwrap.exe', which I assume is supposed to change those settings by itself, somehow became messed up and forgot. I'm not certain if the installation of the other GoG game Real Myst is directly related to it, but it is the only program that was installed and used since I installed and used Earth 2150. Has anyone else reported an issue like this involving any other game?
I have not tried to re-install yet to see if that was indeed Real Myst that caused that, but I suspect it had something to do with it.
(Also to note, though Earth 2150 apparently intentionally disables alt-tabbing and the windows key, you can still get into the task manager by pressing ctrl-alt-delete while on the in-game menu, which should enable you to change the affinity.)

SilentCat: I don't think the GOG wrapper sets apps to use a single core as if you read these forums there are many games where the advice is to run with a single core. There are ways of creating shortcuts that do this for you, anyway. Command line prompt options can be used to load a specified application using whatever core affinity settings you have available on your machine.