At first, the current version got cl_maxfps 50 (IIRC) limiter. You can set it to any bigger (or lesser) value, but game is hardcoded to 250 fps max to avoid burning GPU like Starcraft II did.
Second, the game is based on the idTech2 engine, which was designed for the first-person dungeon crawling game, not the strategic "bird's eye" view. So, it really underuses the GPU and overuses the CPU as the result.