As far as I know about this, neither SSG nor SwordShattering are affected by DR. So theses 3% and 4% avoidance are really 3% and 4%.
Now concidering both of them the questions that may arise are :
* With SSG how many DR affected avoidance you can get from re geimming your stuff
* Once gone with SSG can you come back to SS (this is really something I'd like to know, is this rune not something you won't ever drop once got one ?)
* With SSG you miss 2% RS proc, can you afford that ?