[ThunderCactus]

Like I said, it depends heavily on your setup.
For testing, pick the length of barrel you want, you need .20s, .30s (or whatever weight you wanna use), one barrel with Rhop (since it doesn't make sense to have 8 Rhopped barrels), and a few ported cylinders of different ports (diff brands have diff volumes too, so you'd have to be real picky).
Change cylinders until you get joule creep with the heavier ammo, more creep is better. It means there's constant pressure behind the BB, which means it's getting optimal pressure for the length of the barrel. There IS a point where you'll lose fps, where the air won't be able to reach peak compression before the BB leaves the barrel.

Otherwise, you're talking about the minimal distance point of stabilization that's possible. That would require a few barrels and cylinders and BBs to do the same test above several times. You'd be tracking 20-30 rounds on each barrel and cylinder for range and accuracy until you find the point of diminishing returns.

The TK twist barrel has rifles to allow more air to center the BB in the barrel. Just like a widebore does. The actual rifling makes no difference in the range or accuracy what so ever, it's just a gimmick that happened to function like a widebore. If the rifling DID impart any sort of spin on the BB, you'd notice it, and your gun would be horribly inaccurate. You're also trying to impart spin on an object that's already spinning really fast in one direction, so like a gyro, the BB actually resists any other spin that the rifles are trying to put on it.