When we moved to a Pure Storage SAN, one of their boastful claims was their data compression and how good & fast it was. When we compared it SQL Server PAGE compression and presented them with our results... they shut up...
So, in our situation, sticking with SQL Server compression yielded the best results... Both in terms of speed and size on disk... BUT... As Kevin said, testing is the only way to know for sure what will work best in your specific environment.
Did you hit up Argenis Fernandez with your testing and results? I am sure he would be interested in that.
Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service