It all depends on what is installed on the computer and if all the updates are done. Microsoft released a recent update to Windows 7 which helps with current generation Intel CPU's.
However, some anti-virus programs also alter the scheduling for CPU's. Once installed it is permanent. The only way to revert back is to wipe out the hard drive and re-install Windows.
Aces High only uses 2 cores, at the moment. On the other hand, DirectX can use any number of cores. It will also depend on the sound card installed. Some sound cards/chips are single-threaded, while others are not.
There is just too many variables for any one combination of things to hold true for all systems.
Certainly adjusting the priority of the application will help a little, but it may not help at all, again depending on the configuration of hardware and software installed.