Here are the latest times. I was hoping to finish in under 48 hours, was pleasantly surprised.
Hour 1: 8%
Hour 2: 15%
Hour 3: 28%
Hour 4: 40%
Hour 5: 52%
Hour 6: 62%
Hour 7: 70%
Hour 8: 78%
Hour 9: 87%
Hour 10: 95%
Hour 11: 100%
So with enough RAM, the progress stays more or less linear. Did you increase dbcache settings? I'm not sure if it would still matter: Linux can handle file cache on it's own.