A few points to ponder. First, transonic is not really a specific number, it is a range from 0.8 to 1.2 Mach. Second, a bullet from about .8 to 1.0 Mach will have air passing over it that is going over Mach. Consider what gives an airplane wing lift...same physics applies, but in 360 degrees. Third, the disruption magnifies the instability and it is compounding. While mass matters, sectional density seems to matter more practically.
As for PCCs, yes, it does have an affect, and I have been able to show it. Obviously, the less stability the bullet has from shape and spin, the greater the effect. While most .22LRs are 1:16 twist, there is data to suggest that 1:12 to 1:14 twist will give better accuracy out past 100 yards with subsonic ammo. The same is true of PCCs. Anyway, with 1300 fps or so 9mm, you go transonic just after 100 yards. My PCC shoots about 2 MOA out to about 10 yards past the transonic point (120 yards) then it starts to open up. 30 yards past transonic, I was up to 5 MOA and at 50 yards past transonic I was over 10 MOA (200 yards). Same exact bullet and PCC, started out at 950 fps (140 fps below transonic) I was getting a 4 MOA group at 200 yards. Granted I don't normally shoot my 9mm PCC with a Precision optic, bi-pods and bags, but I wanted to see what the practical limits of the 9mm PCC were for several ammo types and velocities. While I have a few loads I have been able to shoot out to 300 yards with good (4-5 MOA) accuracy, it is not practical nor is it fun. About 100 yards is, IMHO, the practical limit and with almost all PCCs and 9mm ammo combos, they should be 5-6 MOA capable at that distance, most better. But few combos can be expected to carry their 100 yard and in accuracy past 150 yards.