The bandwidth available in the PCI-2 spec is more than todays cards can fill (one of the reasons that AMD seldom uses PCI-E 3 slots (to save money, the 3 cards run fine in 2)....PCI-E 3 is more efficient, but will notice little to no difference performance wise - sort of like DRAM (DDR4 is more or less a continuation of DDR3, originally DDR3 wasn't planned to go higher than 1600 - the people wanted faster, and the manufacturers obliged, creating faster - that's why all this new DDR4 has such high CLs)