ph-buffered fertilizer just makes it moer difficult for pH drift to occur, but not impossible. pH simply a ratio of hydroniom to hydoroxide in the solution that occurs.
5.5 is too low in my opinion. it can be fine but probably need to amp up Ca and maybe some other things due to a lower pH restricting availability of Ca (first before other things).
my nutes ph balance to 6.0. this gives some leeway on each side of the target.
you wannt 'maximize' output by some small fraction of a percet, make 5.5-5.8 work, lol. it's not worth the effort. People that think they need massive amounts of Ca are probably running a low pH too and misconstuing cause and effect. or, they consistently get ca symptoms and 'can't seem to fix it' lol. very likely pH related if providing 100+ ppm of Ca in a soiless/hydro context.
oh and if you are i soil.. 6-6.5 is a better target, and yes, the soil can help with ph-drift or it might cause ph drift.. no guarantees there. the wrong microbes flourish and pH will go where they dictate.