My primary concern with any bike frame is the reach or distance from the saddle to the handlebars. Older bikes had short top tubes and were designed after criterium race bikes and not at all good for the average/normal rider. If the reach is too great and the stem is already short then the bike is too large. In the late 80's the rise of trathalons resulted in bikes like the Dave Scott Criterium that have more relaxed geometry and were great for general riding and for touring.
Easy enough to change out a seat post but it will also change your relative position over the bottom bracket which can affect climbing with a bike. But for a very short 7 mile commute this is not important.
One big advantage of a larger frame is more room to mount a rear pannier on a rack and have enough clearance that you do not hit it with your heels while pedaling. I usually ride a bike with a 22" frame but for touring I had a frame built that was a 25" one with relaxed geometry, including the fork rake.