EDIT: It was a mistake, I'll just keep the thread in memory of my stupidity.

I just encountered a quite annoying thing with downloading the game THROUGH THE BROWSER (GOG Galaxy and GOG Downloader work fine). You cannot download the single parts that way, as 4 and 6 are missing (or rather, they are actually copies of 3 and 5) so there's no way to install it after having downloaded them (yup, I tried renaming them to what they should be, it doesn't work).
It's funny that nobody noticed, I guess using Galaxy and Downloader is so much easier that not many people tried the other way. :)

Can't confirm. Part 6, -5.bin, is smaller at 2.2 gig. Using Firefox and all the links are appear to be working normally for me.

You don't need to rename anything if your browser is downloading properly. The filenames should be:

Galaxy installers
setup_the_witcher_2_3.5.0.26_(a)_(10696)_(g).exe
setup_the_witcher_2_3.5.0.26_(a)_(10696)_(g)-1.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)_(g)-2.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)_(g)-3.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)_(g)-4.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)_(g)-5.bin


Classic installers
setup_the_witcher_2_3.5.0.26_(a)_(10696).exe
setup_the_witcher_2_3.5.0.26_(a)_(10696)-1.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)-2.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)-3.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)-4.bin
setup_the_witcher_2_3.5.0.26_(a)_(10696)-5.bin

Thank you very much. I didn't realise I hadn't downloaded one, sorry for the pointless thread.