Croceas grow at an average of 1 to 2mm per month in the wild where they get full sunlight and all the phyto they want. That's a maximum of about an inch per year. 1/4 to 1/2 inch per year is typically in a tank.
Maxima can grow at an average max rate of 4mm per month in the wild (maybe 2 inches per year at best)
Derasa - 6.5mm (3")
Squamosa - 7mm (3.3")
Gigas - 10mm (4.7")
These are averages, so there will be some inidividuals that grow a little faster or slower, but these are also in the wild under sunlight.
The numbers for crocea, maxima, and derasa came from Hart et al. (1998), for squamosa came from Foyle et al. (1997), for gigas came from Crawford et al. (1988) and Bell et al. (1997)