My experience with disc brakes (i dont count drums even a brakes :) )
1985 Golf 2, 8v Gti. weight 890kg/1960lbs
Stock brakes 239mm x 20mm, rear 239x10mm. 9,4"x 0.8" rear 9.4"x0.4" would fade from 100kmh to 0 at 40kmh, 62mph to 0 at 24mph.
Upgrade 256mm x 20mm. 10" x 0.8. brakes would fade away...