Supreme Commander is one of the first games to feature out-of-the-box multi-core processor support. Will a quad-core CPU really show better gameplay? HardOCP has real world gameplay results plus Vista versus XP performance findings with SupCom. Here's a taster:

We were quite surprised at the level of disparity between Windows Vista and Windows XP performance in Supreme Commander. We initially began this evaluation with the intention of using Windows Vista solely. Windows Vista supposedly has better support handling multiple threads across multi-CPUs. This should benefit dual-core and quad-core usage in games that take advantage of multi-threading. After we performed our evaluation in Windows Vista, to be thorough, we decided to evulate Supreme Commander under Windows XP to make validate our results further.

What we discovered immediately was that performance was much faster under Windows XP. It was at the level where we could now run the game with higher in-game settings on dual and quad-core. It is quite clear as can be seen from our highest playable settings evaluation and our apples-to-apples tests that Windows XP is simply faster. However, the same pattern of core scaling emerged that we experienced under Windows Vista. Single-core was still unplayable, dual-core was much more playable, and quad-core delivered the best experience with noticeable improvements.
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These results are quite conclusive; if you want the best gaming experience possible, an Intel Core 2 Quad quad-core processor will provide it. However, if you have dual-core, an acceptable gaming experience can still be achieved. With dual-core it would be more advantageous to stick with Windows XP for now since it provides faster performance. If you are going to run Windows Vista you will have to downgrade some in-game settings which do impact visual quality in the game negatively. The single-core results are very surprising as this game is simply not playable at all on either OS in our opinion. This is truly the first game where at least a dual-core CPU is 'required' to have a gameplay experience.

There is another game on the horizon also with dual-core as a requirement, Alan Wake. We look forward to seeing how that game fares with multi-core as well. S.T.A.L.K.E.R. was just released and it also supports multi-core processors out of the box. Then there is Crysis, Unreal Tournament 3 and Half Life 2: Episode 2 to look forward to, also supporting multi-core processors. It seems 2007 is the year that multi-threaded gaming is going to start shining. If the performance is as pronounced as we are seeing in Supreme Commander we will be very pleased. Still 2008 is likely to be upon us before we see games truly grasp multi-core precessors.