If you are going to go the GFI route, I recommend replacing all the outlets with GFI's. Otherwise, you will lose power to a whole circuit everytime a GFI trips...which can be often if your running an entire house on GFI's. When you install the outlets use the "Line" side only. Then you can replace the 6 breakers with arc fault breakers and you won't have to worry about the old wiring.
Master Electrician, Air Conditioning & Heating Repair Company Owner. www.TECertifiedElectricians.com