There are 3 sets of numbers that matter to an aircraft owner:
1) Useful load, so that you have enough capacity to carry your typical load
2) Overall performance, so that the aircraft has the range and speed appropriate for your typical trip and the runway performance necessary to operate from your typical airfield.
3) Total ownership costs. Fuel use is only one part of the equation. A rough but nevertheless surprisingly accurate predictor of costs is when comparing like performance singles and twins double the cost of the single. So for example a Seminole will be twice the total costs of an Arrow and and an Seneca 2/3 will be twice the cost of a Lance/Saratoga for the same miles flown. I would suggest that for a Cherokee six the same equation would roughly apply. Double the money for approximately the same load, range and runway performance.
The Twin Comanche is a very impressive aircraft with very good fuel efficiency and simple and economical 4 cylinder engines. However the cabin is smaller and the payload much less then a Cherokee six and parts are getting harder and more expensive to find. To equal the capability of the Cherokee Six I would say you would have to get an Aztec.