That is why we ask questions on forums and read what others have to say. It might seem like the OP is being hi-jacked, but it is usually just an extension of the discussion/education.
If a bullet is stable, the barrel will stabilize any bullet that is shorter (lighter), providing it is similarly shaped. Saying that it may not stabilize lighter bullets goes to another factor called tractability and generally becomes important with a 30 cal and shorter bullets at 500 plus.
A 1:10" twist will allow the average 150gr jacketed bullet to be used up to about 600 yards. At longer distances than that, best is to switch to a heavier bullet. A 1 in 9" will allow a 150gr to be used at the same distance of about 600 yards or less, it will not hurt anything, but even longer bullets than 180gr (higher BC) can be used and will have the correct terminal ballistics.
Actually one should measure BC in calibers. For instance a 1:10" twist .30 cal (twist = 32.5 cal.) is tighter than a 1:9" twist .243 cal (twist = 37 cal.)