A Park chain checker is a poor tool for measuring chain wear. A precision 12" machinist's scale costs far less, but all it checks is elongation. That's OK for Shimano chains that elongate quickly, but worthless for Campy chains that can show 1/64" of elongation when they are shot. You need calipers to check roller wear.

If I don't get 5,000 miles from a 10 speed chain, I'm disappointed. I would expect 3500-4000 from Shimano 10 chain and 5-6,000 from a Campy 10. With the new Campy 11, anything over 4,000 is probably acceptable, but I'm hoping or 5,000.

A chain should rarely just start skipping on a used cassette, unless it is so elongated that the contact point with the cogs rises to the very tip of the teeth. That would be far more than .5%. Chain skip normally occurs when an new chain is first installed on worn cogs.