The iGame GTX660 has 5 phases VRM and 2G memmory, with the clock of 980/6008MHz in reference clock model; however, if you press the overclocking model on the rear panel, the clock will boost to 1058/6008MHz for core/memory. The iGame GTX650 has three phases VRM and 1G DDR5 memory. In reference clock model, it runs at 1058/5000MHz for core/memory; and in overclocking model, it runs at 1110/5000MHz.
Source: TPU