Still trying to decide on the best insulation for my house. Some background to help in the process...
Small paid off home,1000 square foot, with very cheap utilties. No plan on moving untill they wheel me off to the nursing home or mortician in 30 years. All ceiling penetrations have been sealed but there's still infiltration issues. New roof with ridge vent and soffit vent around entire house. Pitch is 4/12 with 3' overhangs so the max insulation over exterior walls is 2.5-3" without blocking roof ventilation. Existing insulation is 6" of 55 year old rock wool everywhere except the tight spots over the exterior walls. No vapor barrier. One gabel end and one hip end. Supply duct is in attic wrapped in 2" fiberglass with no vapor barrier. Design temps are 2 and 95, very humid in summer, heating hours are double cooling hours. Can be heavy snow loads on the roof,2x4 construction.

Best application for this house would be?
A) Spray foam underside of roof deck eliminating venting
B) Remove rock wool and foam the ceiling
C) Add a layer of batt over the rock wool
D) other- please explain