A few thoughts....

• I think you're being too fussy. I've used a variety of bikes with different gaps and combos -- including 1 x 8 -- and never got upset over hitting a precise cadence.
• If you really can't stand where the whole range of the cassette falls, why not try adjusting the chainrings?
• I don't think there is a big issue with using a 10 speed cassette, especially if you can do your own maintenance.
• Barcons are pretty robust.