Bear in mind that those are really big panniers, made to carry enough stuff to tour for weeks on end. Maybe you carry that much back and for the to work, but with only a milk crate now, I doubt it.
For commuting, I use front panniers mounted on the rear. I prefer Ortlieb's "packer" series to their "roller" series, but it's the same idea and they're about the same size. For my four-day work week, on Mondays I'm usually packed with a library book, a pair of jeans, and four work shirts in one side. There's another library book with four days worth of lunches and snacks, my towel, and sometimes my lock in the other. All this in the smaller "front" panniers.
Tools, tube, and patch kit, BTW, are kept in a regular seat bag for easy access. Good place to keep my keys too.
Front panniers on the rear - great idea! I was a little worried that these would be too big, but I didn't know you could mount front panniers on the back. Thanks!