Do a google search for a heating / cooling load calculator .
The pay back will partially depend on your electric rate per kilowatt hour .
Mine is a bottom of the line 13 SEER unit . I read the high SEER units heat fown to a lower outside air temp .
God bless
Wyr
We self installed a mini split last summer . I looked at the brands that used a " quick connect " system . They cam at a price premium over the ones that used flare fittings . I chose the flare fitting due to lower cost . Plus I had the vacuum pump and manafold / hoses / gauges .
God bless
Wyr