"Will I gain some speed by adding a separate physical harddrive to prerender only (and maybe final render) instead of using the same drive as the media is on?"

Hard to say in exact round figures, Ulf? However, keeping the system drive separate from rendering is a good thing. Having "another" drive to render to is a good thing. Having an external is another way. But what I/you/we need to get a hang of is that there is a lot of maths going on when rendering. This can be a variable. The rates at which the this render is plopped onto the drive is another variable but is influenced by the spindle speed. It doesn't take much to recognise that render and write speeds might start to approach each other. So, and notwithstanding these variables, having separate drives for pre- and render APART from the media drive has to be a good thing. But again, it will depend on just how much and how often.

Bottom line for me is that I have separate System , Pre-render, a render and separate EXTERNAL original media drives. It works and until I get some more exotic setup it has worked very well. Now do I get better render speeds having the drives separated out? I have to say I have a better CHANCE of this happening than not.

As I do more of this stuff, more drives are better - in more ways than than this. If you want to check out typical rendering speeds against you system, our chums here will provide a plethora of Vegas sites that you can download RenderTestVeggies.

Hope this helps - Ulf?