I used to use only .060 for the same reasons mentioned above, but now I find myself prefiring .080 Boltaron. You still get nearly as defined of a form, but that extra .020 really stiffens things up and IMO makes a favorable difference in retention and the overall fit of the sheath.
I've used it for small, medium, and larger knives alike.
I'd suggest getting a square foot of both and seeing for yourself.