The WD30EZRX is a 5400 RPM drive whereas the WL3000GSA6472 is advertised as 7200 RPM.
I would compare your drive's benchmark against the following:http://www.sakura-pc.jp/pc/snap/hdd/WD30EZRX/WD30EZRS-HDT6G01.pnghttp://img651.imageshack.us/img651/5864/hdtuneproahcibenchmarkv.png
Notice that the spread of data points in the access time graph is about 11 msec. That's the time for one complete revolution at 5400 RPM ("IntelliPower").
I would also examine the 2060-xxxxxx and 2061-xxxxxx numbers on the PCB. These are WD's part numbers and should help you confirm whether your drive is in fact a Caviar Green or a Black.