Suggested size for root tip pruning pots.

Hello there! About to start up another indoor grow and after seeing so many good results from root tip pruning I think I'm going to have to hop onto this technology. My question concerns the size of the root pruning pots that I would need. I typically veg for about a month, and the strain I will be growing flowers for about two months. I will be flowering 7-9 of the best ladies (I'm probably going to veg about 30-40) in a 4x4x6 home made box under a 1k watt hps, I was thinking 5 gallon pots would be more than enough, and I am tempted to just get three gallon ones. What would you guys suggest?

Edit: sorry for making two threads, not quite sure how that happened.