Dwarf Fortress is memory-limited, not CPU limited. Running DF on multiple cores won't change the fact that the simulator taxes memory extremely hard. Taxing memory even more by including 3d rendering or PCIe transfers to a graphics card will slow down the game.
Its a known fact that Dwarf Fortress is mainly effected by memory latency (and not cache size or memory bandwidth). Each simulated agent takes up a lot of RAM, and lots of their information needs to be updated in every game tick. Cache-optimization is near impossible.
When the single CPU that runs Dwarf Fortress is almost always stalled waiting for RAM, then adding more cores to the mix does NOTHING.
