Now that the National Rail booking systems have the 2015 fares loaded it appears that there is a good way to undercut the price of a paper zone 1-6 travelcard. As we know, off-peak in boundary travelcards are being withdrawn from Jan 2nd, but out boundary ones will still exist. Epsom has long been one of the cheapest places to get one as Southern offer a discounted version which can only be used on their trains between Epsom and Ewell East. Once you are inside the zones it becomes a normal travelcard. There is no compulsion to use the ticket at Epsom.
So, the £10.50 Southern only travelcard from Epsom will save £1.50 over a zone 1-6 travelcard and £1.20 over the zone 1-6 off-peak cap on Oyster. Ticket offices should sell the ticket if asked, but it can always be bought online and picked up from your local TVM.
Remember that this is only effective once the fares actually change in