After much research I finally ordered up my first Tom Bihn bag, a navy/iberian Tristar. I work at a remote mine in northern Canada and fly to and from work every two weeks on a Bombardier dash 8-100. These planes have a very small drop down overhead bin (probably the smallest one out there) and in all my reading I couldn't find an instance of someone fitting a Tristar in one. I'm happy to say that with a full load (2 changes of clothes,15" macbook pro, chargers, toiletries, 2 bags of coffee, large headphones, Ipad etc.) the bag fit as if it was made for the overhead, but just barely. A good shove was required to get the bin to fully close and engage the latches. With a slightly less full and bulging bag there would be no problem. I wanted to post this in case there were others out there regularly flying on the DHC-8-100 who wanted to get this bag.
As a side note, I really really like the bag, it's very compact yet well thought out. I've gone from a ~20" checked roller to this one bag carry on without loosing much capacity and I have no doubt that the sturdy construction can stand up to the abuse this kind of travel puts on a bag. All of the epic amount of praise they get for quality is justified. Sometimes you can tell right away when something is made to last. Also.. get an absolute strap!