The 640 is very good because it uses 2 high-density platters rather than 3-4 low density platters. This reduces heat and increases speed.
I agree that 1TB drives are the way to go (I suggested the 640 since it was closer to what you were asking about). Of the 1TB drives, I really like the Samsung F1 drive since it also uses high-density platters (I believe it’s the only 3-platter 1TB drive) and you can pick it up for $150.
I have a WD 640 as my system drive and multiple Samsung F1 drives for media in my Mac Pro. Both drives are great.
-Bryan