As far as I'm concerned, multiple partitions is the way to go. You can use small partitions for OS and a large partition for your files.

That said, I've never tried System Picker. The first thing I've done with any Mac I ever used IRL, was to install a larger, faster HDD, internal or external, initializing/formatting/partitioning all my drives with FWB's HDT(ooKit) instead of Drive Setup.