This may not answer your question, but: distance is not everything. You need a fair amount of distance, yes, but you don't need 300 yard drives each and everytime to play good golf. You have to have sufficient distance to hit 13 or 14 greens in regulation - that is it ... nothing more.
Let me give you a practical example: me.
I am 33 years old now and have been playing since I was 13, so that is about 20 years. I first broke par when I was 14, broke 70 the same year and scored a 66,68,66,70 when I was 16 in tournament play. Last year I scored a 65 without having seen the golf course before (and I was using borrowed
clubs without a driver).
My driving distance: 240 yards at 75% power and around 275 yards with a good hard swing. I never hit the ball as hard as I can, never. In the last 2 years, I have gained about 30 yards in distance with various driver/shaft combinations. Before the last 2 years or so, my average was only about 230yds - and I still scored in the 60's and early 70's.
I am just about always away when I play with pros. So what? We all get to hit a drive, we all get to hit from the fairway, etc. But (there is always a but), I normally always hit the fairway, I hit 14 or 15 greens a round and the honour on the tee box is normally mine. If the honour is mine more times than not, who is the leader? Me.
At the end of the round, the winner is the guy with the lowest score, not the guy who bombed it miles ahead of you.
Don't let the lack of distance (not that you are a short hitter) get you down! You have plenty of length to break par and easily too - if I can, anybody can.
Now to answer your question more directly:
If you are hitting to the 250-270 yd mark, you are probably in between shaft flexes. Unfortunately for us golfers, shaft flex is based on club head speed and not distance, so I'm taking an educated guess.
Distance is a combination of: ball speed, initial launch angle and spin rate. To get the ideal combo of all of those you can look at what type of ball you play with, loft of your driver, flex of the shaft, "kick point" of the shaft ... out there is your ideal combination and if distance is what you are after, go and find it. The only way to do that is through a fitting session with a good equipment fitting specialist.
Changing your shaft alone will not add distance I'm afraid.
If you really, really, really, really want to get more distance you would benefit from: 1. a fitting session and/or number 2. lessons from a long-driving expert.
Where abouts in the US are you? I will look up a few names and send them to you for a fitting session.
I know a few guys who teach long driving techniques to "conventional" golfers ... they teach the basics like coil, weight transfer, how to increase club head speed, etc. etc. I'd do this as a last resort.