Next time you are out flying the 'Bus, simply print out the landing data. There, in black and white, from the aircraft itself, you will see that MANUAL BRAKING stops SIGNIFICANTLY shorter than either LOW or MED autobrakes.
That said, VERY FEW PILOTS would EVER think of standing on the brakes at touchdown and thus ANY runway shorter than MED brakes but longer than MAX MANUAL brakes should be viewed with significant skepticism as to landing performance (i.e. stopping on the hard surface), due to unknowns and unknowables.
There are certain runways we use that REQUIRE a go-around if the aircraft is not on the ground within the first 2000' because there is, IMHO, a rather large "fudge factor" that one must apply to any landing, due to the myriad conditions that can affect performance that may not be fully known or understood during the landing planning phase.
Happy Landings!