A quick release seat post rack is pretty convenient. You could split the duty between the seat post rack and a large handlebar bag.

P-clips are my least favorite way to install/remove a rack. I think you would get pretty tired of screwing and unscrewing 4 p-clips (takes a wrench and screwdriver) multiple times a week. You'll probably end up leaving the rack on.

No experience with the Knog rackless panniers. Looks pretty slick. If your widescreen laptop will fit, I'd go with that.