There isn't all that much premium being paid, at least on the 900's. Besides, there is almost nothing allowed in open time anymore. If you want to pick up premium, you usually need to be willing to pick up reserve days. Fo... that's another story.
And for the record a topped out (12 year) captain on reserve might hit $100K if you include the full year's bonus money, and yes 12 years will have you on reserve in DTW or MSP. We don't get the "rolling thunder" or anything close to it here.