Srawperd: For those who don't know how to run the game in higher custom resolutions, refer to this thread first:
http://www.gog.com/forum/simcity_series/high_resolutions_windowed_mode_and_flickering

Decided to post this to help people who wanted to launch SC4 through the Galaxy client rather than just using a modified shortcut. I encountered an annoyance where the client would only launch the game normally instead of through the modified shortcut. So it wasn't running in the resolution I specified.

So what I did, I modified the shortcut located within the game directory as described in the aforementioned topic thread, then I clicked "Scan and import folders" in the Galaxy client (located within the "+" icon) and this seemed to update the shortcut Galaxy uses to launch the game.

And voila, the game runs in the proper resolution. Not sure if this was common knowledge, but figured it was worth mentioning.