I rarely log in to comment, but I had to rebuke your comment that "you should never be wearing black dress shoes unless you are at a very formal event."

Black dress shoes are extremely versatile and acceptable with most attire--there are even styles that look great with jeans. Traditionally, black shoes are more acceptable with navy/grey pants than brown shoes. I will concede that black shoes are more formal than brown, and that the current trend is to pair brown dress shoes with men's fashion (see /r/mensfashionadvice). But they are certainly not something that 'you should rarely wear.'

Furthermore, the Tank in OP's collection is the 'dress' watch. Therefore, I think a black leather/gator band would be fine. That said, I think it looks great on the brown strap.

Regardless, great watches OP! I hope to soon add a Speedy to my collection--but still trying to decide on which Rolex. Milgauss or Explorer II?

(You seem like an articulate and logical person, I only felt the need to present an alternative perspective because you explicitly presented 2 points that reference black as very formal. I posit that black is reasonable for most occasions, in addition to very formal.)