Yes, they were shot from different distance as mentioned above. We know this to be true due to the different focal lengths of the lenses used to get the desired magnification/composition/etc for the shot.
That said, the shot from the 105 is not cropped at all, while the shot from the 60 was cropped -- it was shot in landscape, and I cropped the image to portrait, leaving the nudibranch the same size as shot in the original raw file. I basically just cut off the sides.
I used the 60 a good bit in Lembeh, and I was glad I had it, but I definitely used the 105 a good bit more. If I could only keep one, I would keep the 105.
With regards to the 15mm, is there any real difference between one designated "DG" and one that isn't for underwater use? I understand that designation refers to coatings on the glass designed for digital cameras, mainly to reduce flare.
Having just moved to FX, I will probably sell my Tokina 10-17, zoom gear, and Zen DP100 mini dome and get the Sigma 15 or 16-35 & a larger dome before Socorro in a couple months.
I have a Thinktank Airport International 2.0, and while great it's a bit heavy. The Cinebag linked above is a good bag too, as it appears as a laptop bag and is generally not weighed as a carry on.
Carry on weight is becoming more and more important. Flying with Singapore Air I can carry on two pieces of 7kg each in business or one if flying economy, while Philippine air only allows one at 7kg and they're pretty strict about it, regardless of what cabin class you're in.
A photo vest loaded down with glass, bodies, and so on is a good option evidently, to make your carry on bag appear lighter, then pack it all back up once you're through security and in the terminal, or better in a lounge with less eyes on you!