I've never had any dealings with anything lighter than 55gr bullets, and those will not come apart unless you handload and jack the pressure way (!) up. According to Army tra-doc, the 1 in 7 twist was picked to stabilize the M856 tracer rounds (since the M856 is a bit longer than the M196). BUT they then got the M196 tracer cartridge (55-grain bullet) , but it is just used for training purposes. It has a red tip and designed to trace out to 500 yards.
The M856 tracer cartridge (63.7-grain bullet) is used in the M16A2/3/4, M4-series, M249 weapons (among other 5.56-mm NATO weapons). The M856 is designed to trace out to 875 yards. It is not to be used in the M16A1 except under emergency conditions, and at ranges of less than 90 meters due to the fact that the M16A1's rifling twist isn't sufficient to stabilize the projectile (1 in 12 twist).
1 in 9 twist is an awesome choice for 55gr, and if you're never gonna shoot anything heavier (ie, longer), thats the one to get. But for versatility, a 1 in 7 will more than suffice.