You will get some benefit from using the SATA power connector -- I think it will have better power management/power saving -- although you probably wouldn't notice that other than a penny or two every few months on your electric bill.
As a side note: I believe a true SATA power connector has more wires going to it (includes an orange wire from your power supply most likely) than a PATA connector. So even with a PATA to SATA adapter, there's no way to get that orange wire if it doesn't exist on your PSU -- so I think some feature must still be missing.
My logic: even when I don't know if it has any true benefit, use the "most advanced/newest" thing that my system will support -- so if you've got SATA cables from your power supply, use em. No problem, though, if you can't.