I count my driving as probably the strongest part of my game. If my putting was better, and I didn't have the occasional handful of bad chips a round (which would not be necessary with better approach shots!), my HC would drop dramatically. The one thing that jumped out as a problem with other drivers was that I was not always hitting the ball consistently in the middle of the face, most notably my miss hits were high or low on the face, rather than toe or heel. I still have the occasional high or low hit, but with the 919THI having little to no roll radius (measured loft top to bottom only varies by about 1.5°, where most all other drivers can vary as much as 6°) , I still get practically the same trajectory regardless if I hit one dead center, high, or low.
I don't remember the exact count of other heads we tried, but it was a bunch! I do remember we tried Callaway first, then a couple other box store brands. After noticing the high/low problem, he jumped to the 919THI. After having good results with that, we tried some others, then came back to the 919 again. He had a few 919 heads that were digitally measured so he knew the true loft and face angle, not just what was stamped on it. After different combos of lofts and a few shafts based on my SS, tempo, release point, etc, we went with the 11° head that was 0.5° closed, and the Wishon S2S White 65g shaft assembled to 43.75" playing length. Unless I screw something up like coming OTT or ???, it's point and shoot.