From my experience Rootbound is a load of crap for most mj grows , unless the plant is going to live 6 months or more i wouldnt bother transplanting it & stressing the plant for nothing , search out an old thread by fdd2blk titled something like " Rootbound is a load of crap " or something along them lines , quite a few members including myself posted about our experiences with so called rootbound plants that gave the same yeilds weather transplanted or not , lots of good pics of serious root balls in x small pots .
Before i went full out hydroponic i grew in 5 gallon pots of soil with 1 month veg for years , when Michigan became legal to grow i filled out my grow using 1 gallon pots , at harvest the 1 gallon plants offered the same yeild as the 5 gallon plants & zero difference in quality , after seeing the results i never used 5 gallon pots again , only drawback was having to water the small pots twice a day , the last year i did soil i used all 1.5 quart soil pots on a drip watering system & had fantastic results .