What kind of single track?
I think you would be a lot happier on the 650bx48 than the 700cx43 - this coming from someone who rides a lot of single track on 700cx42 and 700cx50 - the latter is so much better for anything more than mild, smooth, dirt single-track.
267 is pretty low but should be workable if depending on your terrain. What length cranks are you using?