The Sennheiser totally blows the R11 away, at least for my voice. I keep a couple of R11s for guest mics, because they are really inexpensive and sound good, once you e.q. them right. They are especially good for female voices.
When it's important, I plug two Senn 855s into the SD1. Mine goes through the vocal harmony, the other does not. If if I have a guest singer that is more than just a one-song sit-in, it's easier to get levels and e.q. right by using identical mics.
Of course if you use an external mixer, all these problems go away!
DonM