Reporting back - The /etc/apache2/envvars file is the *perfect* place to change the temp folder that Apache uses on load, and avoid an out of space error for biiiig files(see log above). I thought there might also be a speed boost for having the temp folder set to the same driver as the destination folder for Subversion's server-side storage, but there is not unfortunately. Or if there is, I can't quantify it.
- Paul