The Select is going to have a higher fat content than the two grades above it (Choice and Prime), but the choice and prime should have better marbling in the meat. Not sure what you mean by "higher quality." Did your butcher have a grade labeled on them? Higher quality is going to be marked choice or prime. In my experience, choice or prime will tend to take a little longer (they're leaner cuts), but you're showing 2+ hours per pound; that's a little long, usually. You might try using 235-240 for your box temp. It really doesn't affect the outcome, just the time.
Also, if you could provide some details on your prep, it would be helpful. Did you inject or brine/marinate? Was the meat cold, and put in a cold smoker? You mentioned you're not foiling, but are you opening the door at all during smoking? Details help when we're trying to help you analyze what you're experiencing.