This is misleading because in DF usually when talking about frame rates we refer to how fast the game's cycles are progressing (and this can get slow), while yo

This is misleading because in DF usually when talking about frame rates we refer to how fast the game's cycles are progressing (and this can get slow), while your reference to graphics implies frame rate in terms of graphical computation. The game could redraw at 60 fps all the time, it just wouldn't have anything to update until it was done calculations, and that is the bottleneck here.