Quote - I have timed renders with 2 and 4 threads (and also as a separate process) and the render times are IDENTICAL to it using a single thread.  :(  Major disappointment.  Not sure why this would be the case.

Because your CPU only has one core and it doesn't really matter if it's working one part of the image after the other or on all 2/4 parts at the same time. Window's task manager is showing you 50% because hyperthreading pretends that there is another Core ideling around that could do another 50% of the work - but there's no other core, as you just have one... So no reason to be disappointed. You'd be disappointed if you had 4 real cores and would then see them wasted by Firefly's poor multithreading approach you already witnessed with those 50% of ideling.