You made me read the books and refresh memory, appreciate the opportunity.
My previous post is misleading and mistaken to suggest 6/60 gets you level.
The goal is not to skip or replace the QRH table which is used fly level (pretty damned precise). 6/60 will give you a stable and safe trajectory (residual climb) in all cases, irrespective of weight and configuration, engine, winglet and fuselage length, also at different altitudes.
Exactly the case you inquired: Path is safe but you need to act for A.N.C. while the QRH is figuratively out of reach. A procedural gap which 6/60 will bridge gracefully.
LEVEL FLIGHT INITIAL/INTERMEDIATE APPROACH
A320 wingfence CFM engines 60 t (MLW -10%)
clean cf = 5.5 / 54
config 1 = 6.5 / 58
cnf 1+F = 5 / 58
config 2 = 5.5 / 58
L/G + 3 = 7 / 64
LEVEL FLIGHT INITIAL/INTERMEDIATE APPROACH
A320 Sharklet NEO PW engines 60 t (MLW -10%)
clean cf = 5 / 50
config 1 = 6.5 / 52
cnf 1+F = 5 / 50
config 2 = 5.5 / 52
L/G + 3 = 7 / 56
I got advised 9 years ago; for NEO 5.5/55 looks closer to the original concept. But that defies the idea of remembering just one value. I mean, if 6/60 sounds too much with those engines, try zooming on CLB/10 instead.
The 3/60 you mentioned is not good enough with flaps out, resulting in an undesirable combination of sink and acceleration.