If you do play games that frequently load lots of new content from the storage drive (eg: MMO's that load instances/zone portals/etc) a faster drive or SSD is a nice convenience, but not neccessary addition. I use an SSD for OS/apps and HDD for media storage.
Do these games, or are there games that load from storage during game play, or do they take you to a loading screen? I don't mind waiting a little longer to wait for a level or a map to load, but as long is it doesn't affect the actual game play. I'm sure I've played games before that suffered from stuttering because it had to load directly from the hard drive at some stages of the game, but I suspect that maybe more due to lack of RAM so the game had
to resort to in-game loading.
I will also be getting an SSD but will be using this for the OS and program files as well. The 2TB WD Green drive will be used for light media such as music and television shows, and I was going to use the 2TB WD Black for more demanding media such as HD movies, and game installations. However, as MikeC clarified, HD movies will not require a high performance drive, which is good to know.