Given his past success, I can understand why folks want to slot Backes into the #3C position. I am not sure these same people would be thrilled with the end result, especially if you expect secondary scoring from that line. Backes, at this stage of his career, could possibly slot in as a defensive specialist to take D zone draws, clear the slot, block shots and support D for the breakout. When he was younger, he could support the breakout and either lug the puck out or join the rush the other way. Currently, I don't think he has the wheels to play as a two-way pivot.
So, if you want your #3C to be a shutdown center...Backes can get the job done. However, if you are looking for scoring punch from an effective two-way pivot, there are better options.