May still go for the 3.5 ton 15 SEER based on ROI analysis. Also, this contractor's Manual J, which I provided all the data for over the phone, came up with a 44000 BTU cooling load. That's 8000 BTU higher than the lowest of the 3 other Man J's provided by contractors, and about 12000 BTU higher than the Man J that I did online.
Dealer will install a 3 ton if I'm willing to risk it, but ONLY if I agree to a "hold blameless" clause in the contract in case it doesn't hold setpoint in the hot summer months.
Based on avg cooling costs shown on the AHRI site for the models quoted, and the calculations at www.hvacopcost.com, there'd be almost no power cost savings advantage in a 4 ton variable compressor over a 3.5 ton single speed compressor in my house. There's a slight savings advantage in a 3 ton variable speed over a 3.5 ton single speed, maybe $200 a year, at most.