Well Bootneck, when I very recently re-installed BOINC, I did happen to notice this:
BOINC uses virtualization to allow scientists to develop applications on their preferred operating system (usually Linux) and then run them on volunteered Windows and Mac computers. We call these VM apps.
The bold type is mine, just to highlight that particular part. So it looks as if Linux is preferred by some of the scientists who generate and distribute the work units. Perhaps that is the reason you feel that it's crunching faster(?) I'm only hazarding a guess, of course. But if you want to read the full blurb, you can do so here: BOINC Wiki