Now muley, don't go backin up now. You said the PRB is all you ever need. And also why would you want to shoot a saboted bullet out of a sidelock? Or at least something to that effect.
There are several reason why you would want to:
1. With a faster twist rifling you will get better accuracy
2. At equal muzzle velocity the saboted bullet will deliver more violent terminal performance due to expansion. (provided a properly designed bullet is used)
3. More effective terminal performance will lead to quicker kills and possibly better blood trails.