a/c fan blades not turning easily

I'm investigating a new AC system to replace an existing 13 year old Carrier system. I'm trying to determine if the new high efficiency 2 stage compressors are worth the additional cost, which generally seem to run about 30% more that the single stage compressors. I'm looking at mainly Carrier or Trane units so far. I'm in Charleston, SC with high summer heat and humidity. The current unit is probably a 12 SEER. The units I'm thinking of are the Carrier single stage 14 SEER or the 2 stage 16 SEER, or the Trane 16i. Living area is about 2000 sq. ft. and sizing should be 4 ton based on the people who've looked at it so far. If my summer power bill is now $300/month, how much could I expect a 2 stage compressor to save me over a 1 stage? And is one any more or less reliable than the other type.? Many thanks. Wally

I have a three year old Comfortmaker FBF050B12 single stage gas furnace-A/C cooling my second floor (1700 sq. ft) of a 2 zone system. The first floor is cooled by a larger unit. The house is three years old. During the first three months everything was working fine. During the summer months a violent thunderstorm knocked out my power. When power returned, the upstairs unit was never able to keep up with the temperature. Outside temperature gets up to 95 degrees and inside will be 85. The first floor temp stays at 76 to 78. I have had the installers look at the unit and pronounced it operating normally. I replace the controller board thinking that the power surge could have damaged it, but the problem persists. The air flow is my current target. It has four speeds, and current is set to High for cooling and Med-Hi for heat. The airflow out the vents doesn't seem to be enough, but I have no basis for comparison. Can you tell me a good way to determine if the air handler is producing the required flow? I have recently (within the last two weeks) changed the air filter and I have the units serviced once a year. The lines on the condensers are: large-cool and wet, small- warm, barely, air out of condenser fan warm.