MSI PC Mate Z97 MB has 1 PCIE 3.0X16 and 1 PCIE 2.0X16. Is the performance of two 3.0's significant? Im upgrading from an ASUS Sabertooth 55i and i7-860 with the now obsolete chipset. I bought another 7970 to Crossfire but after installation I was very disappointed. The performance gain was...