They started with 8/32" of usable tread (10/32" - 2/32" legal wearout). After 40k, you've eaten through 5/32", which is 8k miles per 1/32" of tread, and you have 3/32" to go. If they keep wearing at the same rate, you should have 20-24k miles before they get to the wear bars which is, frankly, pretty bang-on to their stated warranty.
It sounds like you're like me, and you replace tires before they're legally worn out. I usually start getting "the bug" at about 4/32" of tread depth, which is right where you'll be in another 10k miles.
I'd be satisfied with that wear trend, yes.