I know that overcharging is bad... but I have never seen anything mentioned as to how much over specified charge the effects start being noticed....

On a system which needed 32oz of refrigerant... would 3 oz, 5 oz, 7 oz, ? start making a difference .... and where would it make a difference ? Would it just be on really hot days where the 'reserve' cooling capacity was exceeded ?... or would it be that the compressor had to work overtime at higher load and thus was at risk ?