In practice, Supreme Commander 2 cannot use all CPU cores. So one interesting question becomes whether we can we can reduce power consumption by disabling some CPU cores in the BIOS. The first chart below shows the different stages of disabling cores. On average, you can save up to 28 W overall by slashing the Core i5 down to a single core. Of course, we don’t consider this a worthwhile and realistic scenario, but the results are interesting from an analytical standpoint.
In the second chart, we disabled CPU cores in the game Anno 1404. The difference between two and four cores is the only noteworthy one, since the frame rate drop is rather large when going single-core. Thus, the power savings isn't worthwhile. If you don't want to play with reduced frame rates, you should stick to two cores, saving around 13 W on total system power.
All measurements are taken at the power plug. The Cooler Master RS-850-EMBA power supply we used features about 82% efficiency.