27" wheel frames with 700c wheels and extra long reach calipers. Typically can fit 35s with fenders, and you get a lower bottom bracket due to the smaller wheel diameter. Longer chainstays give you good heel clearance for bags--probably better than an old MTB frame. Maybe stick a couple extra little braze-ons on there (another bottle cage, fender eyelets, what-have-you.) I did this for a commuter and have been loving it.

One little additional mod I am thinking about is brazing in a second top-tube, several inches below and parallel to the first top-tube, because my frame is quite tall and therefor a bit noodley. Thinking I could stabilize the main triangle by making it smaller this way.

Like this: