I am wondering what some of the symptoms of too-tight rifling twist are.
It's not really something most people need to worry about. Generally the problems occur when people push the envelope in one way or another.
With that in mind, here are some of the issues that may be encountered.
1.
http://www.bergerbullets.com/wp_super_faq/why-do-you-recommend-the-slowest-twist/ According to Berger bullets, spinning a bullet faster than is needed "can amplify any inconsistency in the bullet" which may result in some level of degradation in accuracy.
2. In extreme cases the bullet may be spun so fast that it can't hold together.
3. It's possible to create a situation where the bullet is "overstabilized". It's not usually an issue at short ranges but more of a problem as the range stretches. What happens is that the bullet is spinning so fast that it resists changing orientation to follow the arc of the trajectory. We know that the bullet follows an arc--it starts out aimed upwards a little bit, then at midrange it levels out and then it starts back down toward the ground as gravity pulls it downward.
A properly stabilized bullet will point in the direction of travel--there's enough spin to keep it generally oriented correctly (prevents tumbling) but not so much gyroscopic force that the air resistance can't keep the nose pointed in the direction the bullet is actually going. So the bullet points up when the bullet is going up on the first part of the trajectory, level when it's level briefly at midrange, and down when the bullet starts back down. The spin/gyroscopic force keeps the bullet from tumbling and the air resistance keeps the nose pointing in the direction of travel.
If the bullet is overstabilized there's so much gyroscopic force that it won't allow air resistance to re-orient the bullet as it travels its arc. That means that the bullet is now not as efficient a projectile as it should be since it eventually ends up being pointed a little bit away from the direction it's actually travelling. If it starts out pointing a little bit up, it stays pointing in that direction all the way to the target. Obviously during the level and downward parts of the arc, the improper orientation increases air resistance and decreases the ballistic coefficient of the bullet.
Could a 2.9" barrel sufficiently stabilize the 28gr-31gr 5.7x28mm bullets?
The spin required for stabilization is a function of the length of the projectile, not the weight. We often talk about it in terms of weight since, for a given caliber, bullets of similar construction which weigh different amounts are generally different in length as well.
However, not all bullets are made the same way. A .224" 28gr bullet with a steel core will be longer than a .224" 28gr bullet with a lead core, for example.
What stabilizes a bullet is spin rate. That is, how fast the bullet is spinning. The spin rate of the bullet is dependent on the muzzle velocity and the rifling twist rate. For a given rifling twist, a higher muzzle velocity will result in a faster spin rate. For a given muzzle velocity, a faster twist will result in a faster spin rate.
So with a very short barrel, the muzzle velocity might be so low that the rifling twist rate that stabilizes a given bullet in a longer barrel (with a higher muzzle velocity) wouldn't be sufficient to stabilize that bullet in the short barrel.
It's not a difficult calculation once you have all the variables figured out. Fortunately other folks have worked the problem for us.
http://kwk.us/twist.html
You will need to know the muzzle velocity to work the problem.