Doug, we seem to share similar swing speeds & I have been fit for 910, 915D3 & my current 917D3. I am also a senior player (7 handicap). It is not an offering now as Mitsubishi has moved to the Tensei, but I play the D+ whiteboard 70g stiff shaft in my driver based on the feel & low launch characteristics. It provides a “soft” feel even though a stiff profile, & the consistency is excellent for me. I have demo’d the TS3/4 with different shafts as well as my existing shaft & still the whiteboard wins. I see them available online so would not break the bank if you just want to tinker. You could probably find a trade in 917D series that has the same shaft & try it out for no charge with your current driver head. I had my driver shaft cut down 1” three years ago & increased to the 14g weight & as far as distance/location, I typically am playing my second shot from 240-250 off the tee in the fairway. My natural flight is a slight fade but I can hit a draw as well.

Doug
I could have wrote that!!!
I was fit with the same shaft in stiff for a 9.5 degree TS2 driver, and the same regular for the 3 wood and 19 degree hybrid. I have a U510 4 iron with the Hzrdus smoke 5.5 that I love off the tee but probably would do better with a little more loft on fairways. I kept several of my old driver shafts, and I have swapped out between a Kuro Kage reg, old Fujikura Fuel reg, Matrix White Tie stiff, Diamana Blue stiff, Fujikura Six stiff, and Even Flow Blue reg. Most times I played the Tensei stiff, or the Fujikura Six (1/2" shorter) and would get about the same distance but a little more accuracy and less spin with the Fujikura. At 64 years and sporting several old leg injuries and a crooked knee, my typical drives run anywhere from 230 to 250 and that is fine for my game. About 8 months ago I hit a TM with a stock Ventus Blue, and while I didn't like the results too much, being a big Fujikura fan, the shaft peaked my interest. In August I bought a lightly used Ventus Blue 5R with Velocore that was tipped 1/2" and playing 1/2" shorter than the Tensei. Got it at about half price of a new one with the grip and tip already installed. Little lower boring flight, way less spin, so bumped it up to 10 1/4 degree and got straighter shots but not much difference in overall length. Two weeks later I won a 2 man BB tournament (luck more than skill) and first place was a new TS2 at 10.5 degree with the Kuro Kage shaft. It sat in the corner of the living room for a month before I took it out to the driving range and started experimenting. Ended up playing the Ventus and the 10 1/2 degree head as best performing, hitting lower boring rockets off the tee and tons of roll. Maybe 10 yards gain over the Tensei, and pretty accurate. Not much playing during winter here in Reno, NV so we do road trips every other weekend depending on weather to Northern California. New Years weekend we played and I bumped the 10 1/2 to 11 1/4 degree to get a little more loft to see what effect it would have with the Ventus. Coincidentally I started my warm-ups with my new Orange Whip. Pleasantly surprised! Played 3 rounds now with that set-up and one common thing I kept hearing from my golf buddies was WOW!!! Normally I am one of the first balls we get to on the fairway (they are all 10 years younger than me) but now I am either right there with them and many times a bit further out. I've sold or given away a few of my old shafts so down to 4, but with my experiences the Fujikura shafts are lower spinning and a little tighter on accuracy, with the Project X coming in second. I don't know what shafts are available with the new drivers, and there is always a new one with different performance coming out, so give as many as possible a try. And as I'm sure you are aware, they're all interchangeable so having a few extras that worked for you before creates a huge plethora of options.