DL definitely for the upgrades. Even as a DL silver out of MSP I've had pretty good luck on upgrades. As far as CO goes, most of my CO flying is on jungle jets, so not much CO upgrading for me. O my main line flying, Ive had 2 trips that were entirely mainline, one was paid F, the other I was upgraded IAH-LAX on a 753 on the way there and LAX-IAH (753) and IAH-MSP (735) on the way back. I think it was unusual, even after I upgraded F was 14/24 and 3/8 for seats filled.