I'm planing on getting 1TB HDD for editing. I have 320GB right now on my secondary disk but want room to expand. I'll probably use the 1TB for editing and use my current video HDD for archival. Should I get an external or an internal? I still have 2 open HDD bays so I was figuring I'd go for the cheaper option and get a WD caviar or something similar. But some people seem insistant about using externals as a primary editing drive. Thoughts?