The Milgauss is an interesting piece (and very rare for a Rolex), but the second hand and the color of the markers have always thrown me off.
I was thinking of staying with the 36mm. I have a 6.5 inch wrist and to me, the watch is almost too simple for it to look good at 39mm (don't know if that makes sense)
Yeah 36mm is a good size to me, and both the Explorer and Datejust are that size. I feel both can take that sort of abuse, but some days I feel I would prefer the slightly dressier appearance of the Datejust, and the other days I feel like going with the Explorer 1 as it isn't as ubiquitous as the DJ. Or maybe I should find another piece that speaks to me
As for the Milgauss, its a nice watch, but only the vintage models are rare these days. The current Milgauss isn't rare at all. Still its a good watch and a bit different from the DJ, if you don't mind the color and second hand.
I agree with Frills, the 36mm ref 114270 Explorer 1 is a great watch and very versatile. I bought one more than 10 years ago to wear as an interview watch. Clean, simple, nicely balanced in feel and appearance, easy to read at a glance, and its and iconic part of Rolex history (having been worn decades ago to climb Mount Everest and having greater water resistance than DJs back in the 70s). When compared to 36mm Datejusts of say the 2002 -roughly 2004, the Ex1 has the solid end links and an oysterlock clasp that is better integrated with the bracelet. The bracelet of later Datejusts improved when they revised the model and gave it solid bracelet links, but it became too shiny IMHO with its polished center links and polished lugs (which I find look too rounded). The Explorer 1 is obviously not a pure dress watch, but it looks great with a suit and I liked that while it has a family resemblance to the DJ, it is a professional model with history and design that is as important as that of a Sub, GMT, Daytona etc.
Good luck with whatever you decide.