Intel’s Hyper-threading Technology enables multiple threads to run on each core to efficiently using processor resources. It could be turned ON or OFF through the BIOS setting.
Many simmers suggest to turn it OFF since some argue that hyper-threading generates extra heat which drags the performance of FSX. Others report that stutters are experienced due to extensive collisions between threads.
However, in my case with an i7 930 CPU overclocked to 4.0GHz, with or without using AffinityMask, I find FSX is running smoother with the hyper-threading feature enabled.
Worth a try to decide whether Enable or Disable the Hyper-Threading is best for the sytem.