Our pleasure!
As for the stuttering when quickly zooming in and out, that actually might be due to it having to recalculate the icon groupings at the different zoom levels, not sure.
Regarding the 4 cores, that might help marginally (with things like sound/music playback, etc), but in terms of the main meat of the game that's only for 2 cores. Basically, the main drawing and simulation cycles happen on a single core, and then all the hardcore AI thinking happens on a second core, and then any other minor threads (sound effects and music being big ones) are on hopefully the extra cores.
So there is some incremental benefit to having more cores than 2, but most of the benefit, by far, comes from jumping from 1 core to 2.