Cache/buffer rpm and nas

[ted_chou12]

Hi, I am thinking about buying a new hard drive for mainly the purpose of connected to a nas machine (network storage), large sized, about 2tb. I am not sure whether or not I should be focusing on a higher rpm or a higher buffer/cache? Since there are so many specifications online, I am not sure what type to look for.
Thanks

 

[MRFS]

http://www.newegg.com/Product/Product.aspx?Item=N82E16822136456&Tpk=N82E16822136456

http://www.supremelaw.org/systems/io.tests/platter.transfer.crossover.graphs.2.png


MRFS

 

[ted_chou12]

My budget is limited, i was only thinking in mind of wd caviar green, from the chart, im assuming that the larger the file to transfer, the slower the transfer rate, but there weren't much models for 2tb ones on the chart.
thanks for the quick response