@ozymandias, I think everyone missed one key word in your setup - DroboShare. Once you are hooked up to one of those, you could have 72,000 RPM drives with 30Gbps SATA connections, and it would not improve your performance one iota over 5400RPM SATAII drives. If you are sticking with DroboShare, buy the Green drives, save a few watts, and stop worrying.
Even if you don’t stick with the DroboShare, as the others say you probably will not see any difference, so get the Greens and pocket the difference in price and power consumed.
I have three Hitachi drives in my Drobo V1 and they run very hot (uncomfortable to touch when they are working hard). I’m worried that their life is being shortened by their operating temperature. I have one Green drive in there which is just slightly warm. This is probably also a consideration, especially in a V1 which has inferior cooling to the V2. Another reason to get the Greens.