So, I had a chance to test my own issue a bit more. The problem isn't location based, as I first thought. I changed some graphical settings individually and narrowed my FPS drop near ground level down to the Textures setting (the first one on the Systems tab in options). Setting that to High causes the severe stutter at low altitudes, setting to medium completely clears the issue. It is a pretty severe difference, and only occurs at low altitude, so in my mind it still fits in the "bug" classification. My system can easily handle the High setting on the other maps.
Anyway, hope this might help someone, somehow!