at idle in traffic closed loop will enable the car to sit at idle at 0.90%...no overfuelling,no borewash, no smoke when you pull off after a 2min wait..

as i said it depends on the map as to how much benifit you see,

but a 0.90% car is always going to be cleaner than a good std map of 2.5%

my car ran 55lb injectors, considerably bigger than greys, and wasnt a million miles off a cat test pass with no cat fitted!