Not utalized CPUs showing different FPS measurements?
Some processes can only be done sequentially (you need the answer to one before you can start the other, physics for example), which means you have to wait for that one to finish. Say that particular calculation only takes a small amount of CPU power to do but needs a minimum number of clock cycles to run. In this case a slower CPU may only need 10% of it's capability to run it but it takes 200ms to run, now take a faster CPU that can do the same task in 150ms. You can't just use 20% of the slower CPU to cut the time in half because the task can only run once the previous task is done. This goes beyond just the multi-threading problem and can exist even in a single threaded core since not every task can use 100% of a core. Now add in other factors like how long it takes to fetch information from the cache or RAM, if there are specialized architectures within the CPU for very specific tasks (like a h.264 encoder/decoder for example), or even how far apart things are in the CPU (the speed of light is absolute) and plenty of other complex factors I don't understand and you start to see why things like cores, frequency, and even IPC or transistor count cannot always predict relative performance.
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