Hey there, ALEMA416!
@RealBeast totally hit the nail on the head with his comment. External HDDs are far less powerful, thus unable to compare with the transfer speed an internal hard drive can provide you with. Moreover, portable external HDDs are not supposed to be constantly in use on your computer because this can severely shorten their lifespan and reliability.
I'd either go with another internal on your system, or use the WD Blue for your software. However, if you really wish to have a fast gaming experience, I'd recommend you to take a look at the WD Black drive here:
http://products.wdc.com/support/kb.ashx?id=In5cxT
It's our desktop performance drive, designed to deliver on the high-end demand of your system.
Hope I was helpful. Keep us posted if you've got more questions!
SuperSoph_WD