Depending upon your hardware and operating system, most implementations of multicore at an OS-level will do some degree of load balancing either intentionally or not.  If I run a single-threaded task that chews as much CPU time up as it can, it'll show up as 25% in the task list on my quad core and the four CPU graphs will hover between 20 and 30%.

It is possible that if the current implementation doesn't run physics and rendering in parallel using multithreading the program is spending a good while waiting for vsync when it could be processing physics for the next frame.

Just set a second place on Level 10, too, same thing.  Are top-10 entries being moderated?