"Pangos is averaging 17.3ppg against non-mid majors (opponents include Baylor, OKSU, Oklahoma, Illinois, WVU,St. Marys, Davidson)"
St. Mary's and Davidson are both mid-majors. But I take your point that he has had some big games against big opponents this season.
The gameplan against Gonzaga is to limit Olynyk/Harris first and cover their guards if they are on (Pangos has his share of off nights too, especially on the road. 2/11 vs Oklahoma, 2/12 vs Washington State, 3 of 11 vs Illinois, 2/8 @Pepperdine, 2/9 @Santa Clara)
Pangos very rarely gets double-teamed due to the Zags strength being inside. Delly has games where he is regularly double-teamed (almost every trip down the floor) because nobody else on the Gaels is doing enough on offense, and its simply the easiest/best way to play the Gaels at the moment.
In summary, I'd still have Delly over Pangos in a heartbeat. Pangos is a shooter, that can facilitate a bit, his defense limited by his size. Delly can run a team very well, can often shoot when his team needs it, and plays pretty good D (being 6'4" helps)