Hitachi tries to differentiate itself by outfitting its drives with 6Gb/s SATA -- even if they can't utilize the extra headroom. As designated by the model numbers, Hitachi's 7K3000 spins at a speedy 7200RPM, while the 5K3000 has a slower, more energy efficient 5400RPM rotation. The 7K3000 is supposedly 27% faster than previous-generation products in PCMark Vantage testing scores, and improves idle power draw by 30%. Meanwhile, the 5K3000 boosts power savings by another 29% over the 7K3000, according to Hitachi's spec sheet.
Hitachi hasn't greeted the drives with a proper announcement yet, so we're not sure about pricing and availability. That said, it's worth noting that the new drives don't appear to come with a host bus adapter like the 3TB Caviar Green, so only a handful of machines will fully support them. To use a 3TB HDD for storage you need a 64-bit OS and an OS that supports GPT partitions, while a UEFI motherboard is required to create boot partitions larger than 2.19TB. If you're a little confused, Hitachi offers an explanation and a handy compatibility chart.