Ah... the Sherman, indeed.
I've already decided to sell my XR as well. Just waiting on a friend who has a Pint to decide whether he wants to upgrade to the XR, or go the EUC route. I'm hoping it's the latter.
At least you don't have to decide right away. Take your time and enjoy what the S18 has to offer. If you have friends who ride or EUC groups around your area, see if you can get a feel for other wheels like the Sherman.
Quick note: You'll notice that it's relatively different riding an EUC without suspension, which might actually make you consider keeping the S18.