We've seen that StarCraft II is a CPU-limited title at the medium detail setting, so just how much CPU do you need to run the game comfortably? Let's start with some CPU-speed benchmarks.
Clearly, the game's performance is tied closely to clock speed. Having said that, playable performance can be achieved even at 2 GHz on a Phenom II X4 CPU, with a minimum frame rate of just under 20 FPS. Let's see if the number of CPU cores has much of an impact on performance.
The number of CPU cores has less of an effect than clock rate, although there is a clear performance deficit once a single CPU core is used.
From these numbers, it looks like you'd want to run at least a dual-core CPU above 2.0 GHz to play StarCraft II. For smoother gameplay, a dual-core over 2.5 GHz should be enough to do the trick. Admittedly, playing against multiple difficult AI opponents might be a little more taxing on the CPU than our benchmark, so if you're upgrading with StarCraft II in mind, we'd recommend the higher end of this spectrum. A triple-core CPU at 2.8 GHz or more should be able to provide all the performance you'd want for StarCraft II.