Lowpost,
Driver length adds distance. Adding 1" equals about 10-12 yards depending on swing speed. A stiffer flex will be needed when going up in driver length.
It's not unusual to see a 3x shaft at 48" or 49" in long drive.
My suggestion, get a low cost shaft Mercury Pro Kevlar it's a little stiff by design and take it out to 46". Then start cutting it back until you find a comfortable length. I've had friends try my
clubs and hit them well. Also add a 5 gram tip weight. It helps to be able to feel thehead at the longer length.
Hope this helps,
GolfBald