PC version already sold between 5 - 10 millions according to stats from steamspy http://steamspy.com/app/582010
Steamspy is useless since steam changed the profile privacy or whatever it was so they can't get accurate numbers anymore, the pc release is no where near 5m sold.
The game had 8.3m shipped before the PC version launched, so it's impossible for the PC version to be above 2.3m.
I'd put the figures at around.
PS4 - 8m
XBO - 1m
PC - 1.7m