In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Every step you move up the ladder in efficiency will save you money in the long run, period. I would seriously consider the 16 SEER unit with the Puron (which is refrigerant 410A). R22 based equipment is being phased out and will no longer be manufactured after 2010. R22 will be available long after that I'm sure but most likley at much higher costs.
I assume the Evolution system you're looking at is an air to air heat pump. These work efficiently down to about 38 degrees above zero. Below that it has to work much harder in the heating mode and the efficiencies drop off dramatically. Because of this you would still need either a fossil fuel furnace or electric resistance heating elements in the air handler (the "inside" part). I would probably question the three year payback statement, That sounds very aggressive and optimistic.
One consideration also, does your electric or oil company offer and incentives or rebates for high efficiency equipment? This can help offset the higher costs of the more efficient units.
Good luck, Rich L