Unless your light pollution is horrific, the C14 will show DSO's better from the backyard, especially with a UHC filter. I live in town with two street lights shining into the backyard and there is still a large difference between a C8 and C11; a UHC filter makes a significant difference on the C11 and would work even better on a larger aperture scope. In falling temperatures cooling will be an issue with the C14 - you'll be stuck at lowest magnification for a few hours.
Buy the C14 and sell the one you like least - of course you might end up liking both and be stuck with two scopes
