Over 1.6M in three months with two singles and people are still convinced it can't top MDNA's lifetime sales of 1.8M. Gagz is flopping by her own standard, but isn't here making a loss or doing as bad as people would like her to.
So it looks like ARTPOP will finish out somewhere in the 2-2.5M range unless there's a megahit to come. That's hardly bad, and if there were another couple of even DWUW-level performing singles (~2M) there's no reason ARTPOP couldn't add over 10M record sales to Gaga's total:
2-2.5M albums + 3.5M Applause + 2-2.5M DWUW + 2M Gypsy + 1-2M single 4.