AGOR did a post in his gallery some weeks ago with some interesting numbers comparing several renders to screen and to disk.

I've been rendering to disk myself, recently, and it is a bit faster. Can't interrupt the render to resume later, but it depends how you want to interrupt... for instance on my desktops and laptop, i've been suspending or hibernating if I need to turn the computer "off".

As of last week, I've been rendering just with Bryce Lightning and rather that now.