.... what codec is the fastest render from the timeline for a quick and dirty proxy that can be used to score music in another application... ? ... TIA for any input ...
Uncompressed is generally the fastest. It's probably not the best choice though. I've used 160x120 AVI with Cinepak with good results and extremely tiny files. Set the frame rate to half speed for even faster renders.
If you want a really fast render, you can set the quality for DV to Preview (in the Custom section of the Render As dialog). Render to a second physical hard disk (makes a BIG difference in speed).
Regardless of the codec used, always set the Render As quality to the lowest settings. The speed difference is substantial.
[Edit] You can also set the project settings down to 320x240 and render at lower resolution. That should speed things even more.