lui_gough is right... You're not just ripping, you're shrinking the disc at the same time. This is a way more CPU intensive task than it is memory intensive, but that upgrade definitely can't hurt. Cheaper By The Dozen is a comedy, and maybe you removed extras and it didn't need to be shrunk, or only needed to be very little. I, Robot is a long action title, which would most definitely need some shrinking.
Oh, and the simple newbie mistake is that you're using DVD Shrink.