It depends on your comfort level in terms of weight. I know I am used to Project X 5.5 shafts, and changed the S300 shafts that came with my 716's. This allowed me to play a club weight that felt good to me. If you really enjoyed the ball flight of the old S300 shafts, I'd consider switching, but keep in mind how long it has been since the switch. Your swing might have changed, and this can lead to off center hits for a couple rounds/practices. I hope you make the right decision!

-Joe

Rather than guess what is the best option to lower your ball flight why don't you setup an appointment at a Titleist Thursday event near you or with a qualified Titleist fitter (if there are no Thursday events near you) to hit the current CB irons with various shafts to find the correct one for your swing. Granted the heads are different, but they are close enough to work for the purpose of finding the correct shaft for you. Another option would be to see a good instructor to help with getting your swing back in shape, if it needs it. The instructor may also be able to assist with getting you into the correct shaft.