[KaktoR]

I was able to fast up installation time to ~45 minutes (before it was ~1 hour).

Will upload in a few minutes.

PS: 4xDVD5 is possible too i think, but in this case you must

1) use lolz with right settings (first and last archive was compressed with srep+lzma before and last disc size was about 300mb (without redist). Now last arcive use m1 instead, it doesn't make a difference in Disc number anyway). Only reason i didn't do that was it takes a whole day.
Anyway, lolz is included in both compressor and setup.exe (if you want to give it a try).
Don't forget to change Data# settings inside DiskSpan.bat (sizes!)

or 2) replace Credits.bk2 with a small other bk2 file (f.e. startup_loop.bk2). in this case you must change Data1 compression from lzma2 to lzma and Data3 from m1 to srep+lzma. Furthermore you must edit archive sizes for Data2 and Data3 inside DiskSpan.bat.
At least for english language it could work with 4xDVD5.

PPS: If you want to update the game via steam (or a p2p xdelta), you must restore all files from _backup directory. In case of steam, it will download the whole game again because archive hashes have changed, xdelta will fail obviously because of hash mismatches. Note that!

And make sure your game folder looks like this