I think the 5/8 inch pad is overkill for most residential jobs
Last week in a Denver condo, I swapped out a thick pad for a 3/8 inch one on a glue-down berber, and the homeowner said it felt better than the old setup. Three years ago I would have argued you always need the thickest pad for comfort, but now I'm not so sure it's worth the extra cost for every single job. What's the thinnest pad you'll use on a standard install?
Guess some folks just want their house to feel like a concrete slab. Next they'll be asking for granite countertops that feel like cinder blocks. Maybe we should skip the pad and just glue the planks straight to the subfloor. The client would probably throw a party.