Ammunition quality has more affect on the accuracy. Ammo companies don't load match grade high velocity that I'm aware of, no market demand for it.
The transition from supersonic to subsonic flight causes increased wind drift, by effectively decreasing the bullet's ballistic coefficient. As the shockwave switches positions on the bullet during the transition from supersonic to subsonic speed the bullet's flight path yaws, or takes a minute spiral around the axis of its flight path. This exposes a larger "frontal area" to the air, increasing the drag. So you're really looking at two issues, ammo quality and increased wind drift with high velocity .22 long rifle.
