Does RPM matter when used for streaming?

I’ve got a WD TV Live HD Media Player (already posted a similar topic in that forum, but figured I should double-dip in case someone who doesn’t frequent both boards has some good input), and I’m looking to purchase a new internal drive to store movies on in my computer, but so that my player can access them as well.

I currently have music, movies, and photos stored on a WD1001FALS (1TB, 7200 RPM), but am in need of a larger amount of storage, as MKV files are not very small at all.  I should mention I’ll be using this in addition to the 1TB drive, and am hoping to get a 1.5 TB drive to add on.  I’m pretty much just curious whether, when streaming movies of such a high audio and video bitrate over a wired connection, if the drive’s spin speed is still an important factor in playback, or if the network’s speed (or possible lack thereof) renders any difference between the Caviar Black and Green drives moot.

Money is kind of an issue (insofar as I wouldn’t want the wife to freak out if I bought another expensive computer item), so I basically don’t want to pay an extra $20 for a feature that I won’t benefit from all that much.  On the other hand, I’m okay with it if anyone thinks I’ll get the Green drive home, get everything set up just the way I want to, and become very angry and start punching holes in the wall and breaking windows because it’s too slow.