I spent the last few days putting together a collector's resource for the entire G-Shock "Master of G" line. This includes the Rangeman, Mudmaster/Mudman, Frogman, Gulfmaster, and Gravitymaster. It has charts comparing all of the sizes and capabilities, and I've included as many limited edition watches as I could find.
It also pulls live market prices for all of the models from Amazon, which is kind of fun to see (Red Frogman GF-8250-9JF is $5049? lol)
It's located here: Master of G: A Comprehensive Casio G-Shock Collector's Guide
Would love feedback from dedicated collector's on any errors or omissions, or requests for any additional data you'd like to see. Hope it's useful!