Variation, and Air Space(?)
Mark and Jack: Thanks for the comments! Jack, I looked on the map at the variation you described and it does look really good. I've never been in the Hillier Tunnel. From looking at the map, it appears that the Roller Coaster cuts off a lot of the distance we swam in the Main Line. Plus, as you mention, it's out of the wicked flow, with more to see (the Mud Flats get old quickly!) We will try that one soon, and let you know how it goes.
Mark, are you guys suggesting that there is an actual air space in the Double Domes where you can pop heads out of the water? We didn't see it, but that would be wild!
Thanks again for the comments, gentlemen, and good diving!