I dont know what you are expecting out of this new shaft to justify driving 6 hours both ways and spending alot of money. I am sure there are other aspects of your game that you can work on especially since you are only a 12 hcp.
Whatever you do, DO NOT JUST WING IT. You are a 12 hcp you will not be a scratch golfer with this new shaft. Wait until there is a demo day so you can try out each shaft in your range so you can find the right shaft for you. Putting in the wrong shaft will only make it worse
I dont trust the indoor launch monitors for anything other than swing speed and sometimes i question that. I was fitted on a Flightscope outdoors with Nike and it was very accurate. Trackman and Flightscope are the only ones that i would trust because they have the doppler ball tracking. As a side note it is really fun to see how far you dont hit the ball with a ball tracking launch monitor.
Based on how you described your accuracy faults i dont think a stiffer shaft will drastically make you hit it straighter. It could probably help but not fix. And dont think because you hit a few good PX shots that you should get them. PX are not the most user friendly shaft in the world. Of course if you get fitted and they recomend them then by all means go for it. The articles you read were right about going with the softer flex. Your swing has to be more precise the...