If they were to do a straight trade for Reddick, I wouldn't want to give up a second round pick to get him. Reddick hasn't proven himself in the NFL. I would offer them a fourth round pick. The Cards are trying to dump the salary of a guy that was selected 13th in the draft because they think he is underperforming, they are going nowhere this year, and they want to sign a splash free agent next year.
If they can snag him for a fourth round pick.....hell yeah!
Then if the Steelers are able to deal Bell and get a second round pick or better for him.....they have improved the team, upgraded the team speed and athleticism, and improved their draft for next year.
I would take this scenario in a heartbeat.