Being that you didn't even write a complete sentence, I'm guessing you want to know if that drive will work in your PM G5. I see no reason why it shouldn't, so I'm going to say yes.
But it really doesn't matter, since SATA 2 would only eat that 16MB cache in half the time and slow right back down to the mechanical limit of the drive -- which is below the SATA bus limit.
"reportedly the current Barracuda 7200.9 drives have SSC (Spread spectrum clocking) enabled and are not compatible with onboard G5 SATA and also some SATA PCI cards are not compatible with SSC enabled drives.)"
My understanding (not tested yet) is that the current 7200.9's do NOT work in G5's.