Wally,

I've been on Canon crop bodies for quite awhile ... latest are a 7D
and a 7Dmk2. Was originally contemplating the 5Dmk2 in lieu of
the 7D for a housed underwater system, but passed on it due to
my parallel interest in Autofocus performance for critters, and the
scond generation 5D used the same AF as the first generation, which
had received criticism. Given how pricy the bits are for an UW system,
the 7Dmk2 hasn't yet merited replacing the 7D as the primary for that use,
although for land use long telephoto shots, it clearly is better. I was tempted
some when the 6D came out, but it's AF performance didn't appear to be as
good (reportedly) as the 7Dmk2, so that was the trade.

In any case, this UW use case merited buying an EF-S wide angle (10-22mm),
so I'm not really hurting for a Full Frame for going wide (although I do get
tempted, just because). Ditto for UW macro with a 60mm prime...overall, I'm
not really all that concerned with the prospects of adding a "single purpose" EF-S
lens here or there, as these tend to be good values, even if they're not ever going
to be sold as (or quite as good as) white "L" glass: I typically save up my money for
using it to get L glass on telephotos...currently a 70-200 f2.8 and 400 f/4 ... the latter
will stack with a 7D and 1.4x to be a handhold-able 900mm equivalent @ f/5.6....


-hh