All 3 QBs you mentioned are, IMO, considerably better than McNabb.
If you believe (not saying you do, MDH) that DM has anywhere between 3-5 "good" years remaining, and Philly is in "win now" mode, why not stay the course with DM?
I understand Philly's philosophy of jettison the good player a year early than a year late, but don't you think they have gone as far with him as they could?