Fantasy football trade help trade Joe Flacco for Greg Olsen?

It's a keeper league and I have Flacco, I also have Favre. I have a bunch of mediocre running backs, Ronnie Brown, Bradshaw, Reggie bush, knowshon moreno, shonn greene. I also lost owen daniels so I am thin at tight end, I have dustin keller. Will I be giving up too much if I give up flacco?