I believe MSProxy/2.0 is an email harvester, not 100% sure, but I think I've heard that UA before, and they definitely seem to be hitting you like harvesters do which is all the time. Check to see if they are pulling files that most people can't find on your site (ie. if you have hidden links) because they work on following anything with a path.
I find proxies are the ones that tend to annoy me the most (or at least that I see the most). msproxy has been banned for a while now for me, along with anything that has a ua of mozilla 3.0 (cant remember exact string) as they have the habit of requesting multiple pages per second.