copper or platinum plug on EFI?

Whats benefit of platinum. 2X the life? My SC400 says change plugs (double platinum @ $11/pc) every 60K miles and its been that. Getting some sooty bumper on this. Single platinums are $4, Coppers are $3. changing plugs on this car is a chore: 5 engine covers, and the entire intake tract to the TB. Probably 45 minutes if no brittle vacuum lines break in the process.