After days of reading and debating +/-s, I ended up getting a set of the 40L Caribou Cases. Took a ride up to Roger's shop (garage) in Boulder and spent some time checking them out, talking, etc. I think the build quality, the lifetime guarantee ("you break 'em, we replace 'em"), the maximal usable storage (totally clean inside with no bumps or protrusions), the integrated locks, easy on/off, and total waterproofness (if they can sit in a river for 30 mins and come out dry on the inside, they should be totally fine in any rain i'm likely to still be riding in!) really convinced me.
Hopefully, they don't look as wide on the bike as they spec out to be (39")- and i think the uniformness of shape will do a lot to mitigate that. and at under $800, the bang-for-buck factor is right up there with the HT bags. hopefully, they present less of an aerodynamic obstacle than do the big square alu boxes. plastic is more slippery than aluminum, right?
(will post pics when i get them instaled next week, as Roger is just getting some new bags in today.)