If anything the Berger web site is erring on the side of recommending a faster twist than commonly used. Going with a slightly faster twist isn't going to hurt a thing. But, if you go the other way with a twist that is too slow, it will hurt big time. For instance, 15 twist barrels although not real commonly shot with a 6 PPC can work very well in the PPC when loaded hot and shot in pretty warm weather. But, let the days temperature get down into the 30 or 40's and you might be fortunate to hit the paper at 100 yards. That happened to a friend of mine at the NBRSA nationals at Holton a few years ago. His 15 - 14 1/4 gain twist barrel shot very well in normal summer conditions, but his first group in the UL 100 looked like it had been shot with a shotgun. The bullet wasn't stabilizing at temperatures in the 40's. When he got it home, it went back to shooting well, of course with higher temperatures. I'd say the majority of 6 PPC barrels are 14 twist barrels, followed by 13.5 twist barrels. A 14 twist won't get you in trouble with an understabilized bullet in the 62 to 68 grain range.
The SM does mean Select Match which is the top grade of barrel that Shilen makes. Not sure what the RF is. It's not anything to be concerned with, maybe inspector mark, I don't know. I looked at a Shilen #7 LV contour barrel that I have in stock and it doesn't have the RF mark on it. It just has SHILEN 243 S 7LV 6 SM going around clockwise from the Shilen stamp. Shilen makes 3 sizes of #7 contour barrels. The 7LV would be their smallest contour #7 and is commonly used on 10.5 pound rifles. A #7 HV would be their maximum HV contour barrel that is the maximum contour barrel allowed by the NBRSA rules on a varmint class rifles.