I've got my main rig set to not download any more WCG tasks so that I can uninstall WCG and install the proper boinc client (from which I believe I can choose to run WCG anywise) but holy cwap does WCG ever front load an awful lot of backup work. From the looks of it it might be a few days before it exhausts them all and that's with 12 threads.
I also made the mistake of installing the WCG data on my SSD rather than doing a custom install to my hdd. It wants 10G reserved which is quite a bit on a 120G OS drive, and when I limited it to 2G it filled up over 1G fairly quickly with results waiting for validation and I'm concerned that it'll keep filling it up.