If you're getting a new driver, you should try every shaft available. You're going to get one with the club so you might as well get one that works for you. Very common to hear about people who buy a club with a certain shaft only because of their expectations or what they played before, and then to be disappointed that they are not seeing any noticeable difference in performance. If you can find a qualified Titleist fitter, there are many shafts available and you can pick what works best for your swing. And unless they changed the fitting this year on the TSI, your old shaft will bolt-up to the new clubhead.

Similar specs mean nothing. Until you try it, you'll have no idea how the shaft will perform, and just because the shaft works well with one head, doesn't mean it will perform the same in a different head. A proper fitting with a certified professional on a launch monitor is the only way to figure out which head and shaft combination is best for you.