I don't have enough experience with the 2013 designs yet, to accurately answer these questions, but will in the next couple of days!
I agree that a sweet feature of Coyote 1, is its ability to roll down and become lower profile on top, but still carry a load on the sides. I don't think that has been affected with the addition of the beavertail, but haven't played with one yet, to say for sure!
The new Great Basin has a cable lock pass-through for securing the bag.
I will work with the Siskiyous and have a recommendation for securing them, at the up coming Vancouver Bike show, this weekend.
Giant Loop designs uses tensioned straps as a key to the "framework" of the bag. The shape of the Siskiyou panniers and the design of their mounting straps allow the bags to be mounted securely against the side panels of the bike.
The Siskiyou's mounting system is a good example of the careful design work, thorough prototyping and effective, long term testing that goes into creating a new Giant Loop product. There are many items to consider when "hanging stuff" off the back of a multi-surface motorcycle and THE big one is keeping that "stuff" out of the back wheel and its undulations, while on rough terrain.
Thanks for the questions! Keep them coming