CS:GO is a terribly optimized game (a hack of the L4D2 engine ported from Xbox to PC!), and requires 300 in-game fps in the Source engine for competitive play. 300 fps is the sweet spot for no mouse acceleration and smooth mouse movements, as well as no frame drops on a 144 Hz monitor. CS:GO perf is CPU-limited, and my i7 2600 can only go up to 250 fps on all low settings, so I'm upgrading to a Skylake 6600k.

Blizzard has done a much better job with SC2; one of their goals from the start has been to optimize for low-end computers.