How much / what weight backing, for a wide-use 8 weight?

The Lamson looks nice, but it's also a good bit more expensive.
(Trying to keep the cost on the reel part of this down.)

Tell me this: assuming I do get the V, that should give me plenty of
room for backing. Should I then be thinking 30#, just in case,
because, why not? Or is it really going to be better to stick with
20#, and use the extra room for extra length?