Damn, that's a lot lower than I assumed. I suppose +dmg is the way to go then.
As an aside, I prefer Shotgun Mastery over PU for the higher static +dmg (+80 vs +65 from PU averaged out to include uptime on Energize) because I don't really want to dump IP into RE in order to land perks, much like I decided against Bigburger for FA because of the IP spend and crappy AR with it.
Thanks for the calcs Noobas.