Secondary Weapon Nebbing: Boss % or PDR?

Adding on to what @hadriel said another 30% PDR would increase your damage by 90% against C Vellum who has 300% PDR. You'd also get a 22% damage increase against whatever boss has 170% PDR.

If you intend to do CRA, a single line of PDR will increase your damage far more than another line of %attack.