Bob is right in the post below. Everything is RT until you add stuff that will bring you into the render bar. Drop shadows will put you into the red in a moment. When I just started stacking boxes I got 9 or ten layers of DV. I have not tried any ten bit, but I would expect its at least two or three if not more depending on the complexity.
There are people who would argue that FCP is only ever giving you an RT preview and that everything needs to be rendered (even the ful, light green line RT stuff) It’s nice to have the speed for proofing stuff really quickly.
I say this often but it is true. Ever since the advent of computer based non liniar editing there is one thing that has remained from quadra series Macs to the G5. At some point in my day I am looking at a render bar as it crawls from left to right on my screen. The faster they get the more we push them.
David