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Matt Cutts on dash vs underscore: https://www.youtube.com/watch?v=AQcSFsQyct8

Yeah MozRank to PageRank is a reasonable measure to use. MozRank should usually be about the same as PageRank, so if PageRank is a lot lower, you can infer that Google have applied an penalty to that site and reduced it's page rank. Because page rank isn't updated often, there are times when it's not always accurate, but usually it's a good indicator.