Being a window person (except on the CRJ), I try to board earlier rather than later. Otherwise, I need to trouble Mr. Aisle-- already settled in, headphones on, shoes off, deeply engrossed in a paperback or cell phone conversation-- who's apparently never had the indignity of having to share a row. Once, after about a minute the FA came to ask if there was a problem, then asked me to step into a row to let the pax behind me board... which was a couple rows behind so I had to swim upstream after Mr. A finally won his momentary fight with gravity. Had my train not been delayed and I boarded with Group 1 as usual, all that stress imposed on all parties would have been avoided.

Overhead space is merely a bonus.