in reply to the original post
situation: normal flt/no wx/no atc input/no reason really, to select v/s or lower speed.
except the pilots perception that by doing so one would reach CRZ level faster and thereby enjoy the tail wind for a longer period of time.
lets assume that you are able to select a higher v/s or lower speed at the earliest,say 5000'. assume CRZ LVL 390. normal climb time average (without touching FCU) ~ 20min.
In flying selected speed or v/s, say we get there in 18 min.(IMHO Pffsss)
you end up flying at least 1 extra min of CRZ and have in net total managed to completely muck up the airspace that you climbed through.and spend another minute longer in CLB thrust to attain CRZ speed
If your CRZ LVL is lower and if you only do it from FL100 then, we are dealing in seconds.
these are entirely my take on the situation.
your call