Lower temps will stunt their growth as well as malnurishment. For maximum growth speed the temp probably should be around 80. Humidity levels also effect growth rates. 2.5 at 5 months isn't unheard of. They do go through growth spurts. I believe that the Cranwelli could reach a max size of 8". Just because most only hit 5 or 5.5 some even 7 as females ofcourse. Males can reach larger sizes as well3" to 3.5" for males is the overall average. It doesn't mean that a monster isn't lurking in your stunted female just waiting for the right nutrients to cause an explosion.