Read a forum post once where a guy said he only ever used two wires unless the specs called for the full four.

Oh man, I saw something online saying you're supposed to keep it under 30%... mine's creeping up a bit this month though.

That chert wedge trick is actually pretty smart for a field fix. For a permanent handle replacement, soaking the old one in a bucket of water to swell the wood can sometimes get you more life out of it. If you're putting on a new handle, make sure you get the right size wedge and drive it in good and tight. A little boiled linseed oil on the new wood after helps keep it from drying out and shrinking again.