I had little experience with residential two stage systems until I installed one in my own house two months ago. In my case it's a Lennox XC16 with the Ultratech scroll compressor, and matching evap coil. I kept the six year old Rheem furnace, and installed an Evergreen ECM motor in it this past Friday.
Today is a humid, warm day, with outdoor dew points over 70 degrees, and dry bulb temps close to 95. The system is on 1st stage cooling and is maintaining 74 degrees dry bulb at 50% relative humidity. Comfort is fine. What I'm also monitoring is power consumption, and so far it's much less of an energy pig than my old system. Sized and set up correctly, two stage systems are a great way to go, IMO.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.