Hi Alex,

Congratulations, it sounds like you have found the right length, flex, and grip size for your driver and your swing.  Sure makes a difference to one's game when everything just feels right.  By extending your Pro Launch Red Stiff shaft by 2 3/4" from 42.5" to 45.25" in your driver it will play a little softer than the S flex you were playing at the shorter length and will also change the angle of attack.  Sounds like the right move for you... you can't argue with the better results you are getting.   I have found that there is no standard for S flex or R flex between different shaft manufacturers.  One manufacturers R flex may actually play stiffer than another manufacturers marked S flex and that is why it is so important to test different shafts and find the shaft with the characteristics you are looking for and works best for your swing regardless of whether it says R or S.  

I also have a 909 driver, mine is a D2 10.5* with Aldila Voodoo made for Titleist S - flex shaft, tipped 1/2", 45.5" long with standard size grip.  I find that the 909 D2 10.5* launches about the same or slightly lower than my 910 D2 9.5* with an Aldila RIP a  70 Regular shaft, tipped 1/2", 45.5* length and the RIP Regular shaft plays as stiff or stiffer than the made for Titleist Voodoo Stiff shaft... I do notice extra roll from the 910 over the 909 with my swing.  

I also own a Titleist 913 D3 driver.  I do like the ability to change the loft/lie, even though I still play my 910 and 913 drivers at A1 (standard loft/lie).   What I enjoy the most is that I can change to a different shaft with the 910 and 913 SureFit adapters depending on course, wind, weather conditions and how this old body is feeling prior to my round.  When I bought my 913 D3 with the Graphite Design AD BB SR shaft 46" length, untipped, I had to go to an 8.5* head to get the lower trajectory and extra roll I was looking for.  I will say that the 910 and 913 were big improvements over the 909 for my swing and have given me the lower trajectory and extra distance I was hoping to achieve.  The SureFit adapter is the same on the 910 and 913 drivers.   I hope that the 915 driver will also use the same SureFit adapter as the 910 and 913 driver which will mean that the expensive shafts I am now using will be interchangeable.       

The most important thing for me was to make sure that I hit the sweet spot on the face, usually the best place to make contact is high on the face and just a little inside of center.  Having a driver with a shaft too long or too short along with a shaft that is too stiff or not stiff enough for my swing will definitely affect the results I am hoping to achieve and that is to hit as many fairways as possible and give me the best opportunity to lower my scores.  FWIW, I have large hands and did play a midsize grip for many years but now play a standard size grip which allows me to work the ball better with a draw or fade, if needed... my normal shot with all my clubs is straight.  Always best to get fitted trying different shaft/head combinations on grass and real playing conditions until you find what might work best for you.  JMHO  

Sounds like you are going the right way and... I wish you luck in your search for the perfect driver.  I think I've found it and... then Titleist comes out with something new and improved to tempt me.  Gotta lot of love for Titleist equipment.  Just sayin...

Kris