If I do a project update and get three tasks. (Most recent example today) is there a way to get BOINC to download all the files for one task before it starts downloading files for other tasks so that the first task can start processing while others are still downloading. (Or in this case start and then it would have crashed before the next one finished downloading but that is the way of testing branch tasks!)

No.

Our request (on behalf of CPDN) to be able to control file transfers individually was declined. IIRC, that was at a time when one of the several CPDN regional upload servers was offline or full, and nothing could be uploaded from further down the transfer list until the blockage was fixed. That was eventually cured a different way - every transfer is now always attempted at least once when first set up - and the code that Thyme Lawn offered was never used.

Thanks Richard, I think I did encounter the upload problem many years ago but don't remember reading in the forums about it. I also suspected the answer would be negative because I have never seen posts telling me how to do it!