I think that the focus on smoothnes should include the mouse and how the processor handles the unexpected. How responsive is the mouse on each processor if the processor works hard or if there is very much data that is sent to or from the cpu to other hardware. What happens if one thread is moved from one core to another core etc. If the game behaves as the developers has planned, it may be harder to understand how the cpu behaves.
Personally I think it is a communication thing. The mouse is an I/O operation and I/O operations need to complete before the CPU switches to another thread on that core if it is not made asynchronously. Threads need to be balanced if the cpu should be used effectively. If one thread does more work compared to another and they both need to synchronize, then this will delay both. If something happens in one thread and it slows down, this will slow down other threads until the unexpected has passed away.
Heavy traffic between the CPU and other hardware and the unexpected is more likely to show up.
If you have 200 FPS but the mouse readings are bad, the game will not feel smooth.