I believe your conclusions are pretty accurate and consistent with what I've experienced. All Grizzlies are very tough, except for the 100's which push the limits of the design somewhat IMO.
The 160 and the 190 are the same thickness, however until recently the 190 was substantially harder which made them tougher still. The hardness on the 160 was boosted last year but still not quite up to the 190/150 El Grande level.
Anyway, IMO the 190 and 160 are the toughest of the tough in that order. Everything else 125 and up is a fine head in it's own right. I've used most all of them but have taken more game with the 125 than any other and never had the slightest hint of failure.
Your 160's on steel adapters should be about bomb proof.