As for 1., it is prob at least due in part to the fact that (as you said), you can build Linux to only have software you want ie it's fine-grained. MSWin is more monolithic.
There are always arguments about benchmarking the 2 OS's, but the instinctive feel to me at least is that Linux seems to be faster. Certainly you can run a decent system on a lower spec piece of HW for the same result.
As it happens, a mate of mine is working at a company and recently designed & built a system using Apache/MySql/PHP, originally on Windows. He's never used Linux before, but decided to try it for various reasons. His (un-prompted) comment was that it's definitely faster after moving it to Linux (in his case RH FC3 or 4).
Incidentally, this is quite amusing http://os.newsforge.com/article.pl?s...30222&from=rss