In a way I'm thankful to be 20 miles from work. 4 miles and I doubt if I'd bother. I used to be 12 miles from work and that was actually about perfect (20 miles is pretty lengthy, at least for me). But then again, I commute primarily for fitness ... all the other bennies are nice but secondary.

My cutoff point would probably be around 10 miles. That to me is about where the costs of doing a commute balance the bennies arising from the commute.

Even after 4 miles I'd be sweaty as hell in Texas so I'd have to fulliy invest in showering, packing, etc. That is all a pretty big time/effort investment for only 4 miles in my view.

Good luck on your choices and let us know how it goes. I encourage you to give it a go and perhaps build more miles by taking the long way.