The CPUs can only run two threads per core at a time. Therefore, it doesn't matter if you make more software threads; only 8 will actually run at a time.
All CPU resources aren't actually saturated, as there will still be idle execution units, but since the CPU can't actually dispatch another thread to make use of those units, there's nothing you can do about that.
All CPU resources aren't actually saturated, as there will still be idle execution units, but since the CPU can't actually dispatch another thread to make use of those units, there's nothing you can do about that.