you know, i've been told that the way you preview it affects calculation time.  that is, if you switch the preview during calculation to something simpler like cartoon or cartoon with lines, it's quicker. if that's true, then the difference in the previews (they look different in ways not explained by a change in camera position) could be causing a difference in performance.

i tend to use cartoon with lines when i run cloth sims, and i think that improved the time per frame, but i'd have to check to be certain.