Tuberous begonias are very shallow rooted, and do not be in a hurry to give it a very deep pot. This only means soggy conditions which leads to poor flowering and worst case rot. Sometimes, giving a begonia a "tight fit" is what makes it flower. If you want to replant, you can pot up to an 8" pot and that will create a larger plant, but if it is flowering well in the 6" pot, there is really no reason to pot up until after a few months.

Well, the begonia is still doing well, it keeps growing and flowering. It must like where it is. I've had tie to a couple of pencils (only supporting "stakes" I could find in the office, lol) because it is now getting tall. I'm so paranoid that someone is going to clumsily going to tap it and make it fall and then cause it to snap. It seems that the plant is getting top heavy but I'm afraid of transplanting it and snapping the stems. I think I should just leave it alone, this is the first tuberous begonia that has actually lived this long. This has been a great learning experience though and I think that I will try growing some new ones come February or early March indoors and put them outdoors in mid April or early May before it starts getting hot again.