The overhead bins on both the E-175 and CRJ-900 are not as high and not as deep as those on the DC-9's.

And if FC is full, the bins will fill up a lot quicker than on the DC-9 or any other larger aircraft.

Board early and give it a try, but if it doesn't fit, it just doesn't fit! I had no problems with a soft-sided duffle bag a couple of weeks ago. And as I boarded the GA remarked that I should have no problem finding space for my bags because there were only 5 people sitting up front. This leads me to think that carry-ons have already become an issue and they are aware of it.

Good Luck.