In my Dell lappy, I did have to use the "small chunks" method.... I would melodyne one part (verse or chorus) at a time.... occasionally I would tempt the fates and hit the entire track.... and sometimes it worked fine and sometimes it crashed.
In the new (3+ years old now) tower DAW, I can easily hit the vocal track to any song in it's entirety and edit it without problems. I still click on the "save" button at periodic intervals just out of habit in case something goes off track and glitches ...... It is, after all, running on Windows...