You have to remember that backing on a reel isn't there just for long runs it also helps fill the reel to keep your flyline from getting small tight wraps around the arbor . Sometimes the line can get wrapped over its self in a way that can cause a real problem. I would put all the backing on I could but make sure it doesn't interfere with the operation of the reel.
There will be days when fishing is better than ones optimistic forecast, others when it is far worse. Either is a gain over just staying home.
**Roderick Haig-Brown