man i dunno.... IMHO i think you will be alright for a while. I just was looking at a guys grow with a little tupperware container maybe half that with a foot and a half tall plant a month into flowering showing no ill effects of being root bound.
Your roots really are looking for spots but in the current pot you have probably are far from being root bound. Either way, it may be a difficult transplant. If you are able to cut into the pot I would think maybe to cut it completely in half, top to bottom, accoss the bottom, bottom to top like an apple cut in half. It should be easier to take the "shells" out from each side and leave it intact when putting in the new pot.
I would imagine it would be difficult doing it at this stage because though the roots will be growing out the bottom they still have a lot of room to grow.
In comparison, I grew a plant a while ago that ended up being a full two feet tall (or more?) with that same exact sized pot you have shown above. It did not get root bound and show any ill effects until it was that height, so I would not be concerned at this point.
Anyone with more experience chime in?
****EDIT - damn it, i read that post without scrolling down and seeing you already transplanted! Shit im not even smoking and i got confused.............
Maybe i need more sleep.......
