I still use a Core i5-750 (slower, but from the same generation as the 950 and 960), and still have no trouble keeping 50-60 FPS in basically every game. As for heat, the i7-950 and -960 have approximately the same TDP as an AMD FX-8350. It'll be hotter than a new Haswell chip, but it should be no problem to keep cool with a reasonable cooler and airflow.