I am trying to make my PC as cool as possible(mainly use it for music and movies). Right now I have a Seagate 350 gig 7200.10 drive as my boot drive. I don't care about boot times, but if I used a green drive as my boot drive would loading apps like winamp or firefox be slower?
A new 1TB drive is pretty fast.
There are two main components to hard drive speed:
1) average read speed
2) Seek times
You want 100MB/second+ maximum average read speed. Seek times have to do with the mechanical head taking time to move around. The SMALLER the file sizes read or written the SLOWER the overall speed is. For example, if I had two 1TB drives it would be possible to get up to 100MB/second for a 100MB file but a folder of pictures might drop to 5MB/second.
The WD Green 1TB WD10EADS is an excellent drive. Again, access speeds are important.
FYI, my WD300GB Velociraptor has 7ms access speeds (twice as fast as the best of these high capacity drives). Still, it's quite expensive. With only a single program (like a game) loading the AVERAGE READ SPEED is the relevent thing. Basic multi-tasking leans towards access speeds as the most important thing.
Access speeds are why Solid State Drives are so awesome (the good ones anyway). I'd wait another year but then get one that has over 250MB/second read and write.
The current SATA2 is 300MB/second. SATA600 is going to be released in desktop motherboards in Q3 or Q4 2009. SSD's are quickly improving in quality and speed and dropping in price. I'd love a 500GB, 500MB/second SSD.
You could probably see a difference in application load times between a WD Green and a WD black drive, but I doubt you'd actually notice the difference in real use. Music and movie files depend mostly on sequential transfer rate, and both types of drive are way faster than what's needed to play them.