This has been answered before - and if the site actually had a search function I could go back and find the exact answer!
Anyways, IIRC, coverstock ratings are fairly consistent. The rating takes the strength of the core AND coverstock into consideration. So, the S70 on the Break/Eagle may not be the same coverstock as another cover/core combo rated at S70, but the overall strength would be similar.
In a way that is confusing, because it's almost like other company's "hook" ratings instead of an actual rating of the coverstock.
If I'm wrong I'm sure somebody will correct me.