I will echo the comments from 500WE. Over the years, I have personally owned/shot/hunted with over 20 SSK barrels. Never had a problem and all performed flawless to their level of application. SSK is top-notch in my book.
Do not have any experience with the GNR line so can not inject an opinion.
Taking an SSK barrel (223) to Wyoming in a few days to whack prairie dogs. This barrel rivels my XP-100 223 and that takes some doing.
Best of luck with whatever you decide.
Mark Hampton