Yes sir...it is the yellow dive strap from Doxa for the modern Sub 300

I go for #5 at the largest or ideally #6...I have a 6.5" wrist and have worn Submariners and GMTs for years at 40mm, but lately, my collection has been trending toward 36mm and smaller because they not only fit much better, but also they are MUCH more comfortable.

Great choice! The Santos Medium with the white dial was my first Cartier...super versatile!

Any pics of the Tank Louis Large on your wrist? That is the next one on my list:)

I have a 6.5" wrist and wondered the same thing about the OP's question...I think the Medium size is a much more proportional and overall better fit on 7" and under wrists. The OP may have much better luck with the Medium.

If you want to learn about the history of the Cartier Tank in particular, check out "The Cartier Tank Watch" by Franco Cologni

Cartier is really making some great watches lately...great minds think alike...I also have the Tank Must Large and it is my newest and most worn watch lately. It is just so light and comfortable...much more versatile than I ever imagined!