Speaking purely about PC version on GOG it is around 25-27 GB.... I believe that this whole 40+ GB was an universal estimate if you would install game together with all possible language voice over packs included on the discs (each of these weights 3 or 4 GB) but I'm not the best person to ask as I didn't prepare said requirements myself :)

And before you will ask - no, I don't have the predownload date for you, but it will not start during the weekend for sure (at the same time it won't be "at the last possible moment" either).