I see. Well here is what I would expect from Vegas: (Pulled directly from my backside, so buyer beware.)
It SHOULD work similar to realtime DV preview via firewire. Those who work with Vegas would know that means that you will get a surprising amount of realtime preview until the computer can no longer handle the load, at which point Vegas begins to dumb-down resolution and/or frame rate in preview depending on your settings. So yeah, it’s RT, but it’s not always perfect. But like I said, I think you will be amazed at what it does all by itself.
The grace with which your computer handles the tasks are mostly a function of your memory, processing power, and the speed of your storage. Vegas 6 is reportedly much more able to take advantage of HT and Multi-processor environments, but the jury is out on this one. (Give us all a few days to deliberate.)
I do a lot of SD work on a 2.8 HT machine with IDE raid and a gob of RAM – and I often sit and render sections to get a good look at my work. Other times I am perfectly happy letting the machine drop to 15 FPS, or with trickier sequences scrubbing the TL to see my changes and letting it all render out when I’m through. I’m due for an upgrade pretty soon, and am hoping for strides in multi-processing with the new rev of Vegas.
That’s my best guess.
Ron