Both are beautiful boots. I do think the Beckie will work with dressier ensembles, not just casual. I see them with jeans tucked into them, or with a skirt or dress. I have a pair of boots very similar, except without the buckle detail (which I adore!), and I get lots and lots of use out of them, dressed up or down.
The Mojave is more dressy, perfect for skirts and dresses, and moc-croc is not too much. It adds textural interest. You could wear these also with your darkest-wash, dressiest jeans, either underneath your bootcuts or with skinnies tucked in. It would be a dressier smart casual look. I have found that this color also works beautifully with gray slacks and skirts.
However, what is your shaft height? The Beckie's are 15 inch and the Mojave's are 14 inch. Isn't that a big difference? I would just worry that the Mojave's may be too short and hit at the wrong part of your calf? They seem to be intended as more of a sleek boot than a slouchy one. I think you want the Mojave's to hit up fairly high on the calf? 14 inches on me would work... but I'm only 5'0" so this has me worried because I know you are taller than me!