WD10EZRZ vs. WD10EZEZ

Can anyone explain to me why these two disk have different spindle speed, but the same read / write speed?
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Hi, I have no idea why they have the same read/write speed, maybe support have some information on why is this.

Maybe the controller of hard disk is bottleneck.

WD decide to have two blue drive, instead of green and blue drives. WD10EZRX was the part number for the green drive. It can run at two different speeds. I prefer low power, gamers prefer not to buy. So two blue drives one at 5400 and 7200 rpm, Without any change in rpm. I hope you get a chance to read this explanation, SergeyVsInko
Regards Victorjr