A 320 will always fly to CAT C minima regardless of :
weight, temperature,wind,QNH,elevation or indicated airspeed on short final.
The previous poster was right regarding A 320 stall speed calculation, though a littel bit out of the topic.
CAT is based on REF SPEED (1.3 Vs or 1.3 Vsr/Vs1g) at max certified landing weight. It will depend on aircraft characteristics,for instance a not very heavy aircraft like the CRJ is CAT D cause the ref sped is high due to the lack of slats. As a rule of thumb the heavier aircraft type the higher category.
A 320 CAT C., A 321 CAT D