That's all not taking into account the FPS. It's already suboptimal at 60x60 base defense, esp with lots of smore/fire. Quadrupling that will not exactly kill it, but still.. What would surely kill playability is adding z-levels to the base maps. No way around that but for rewriting the renderer, and with the scripts, I'm not sure it's even possible.
You want Dwarf Fortress-like bases, you've got to rewrite the battlescape.