It definitely works on Steam as I did it when I was building my new PC and also debating what I was having on my SSD etc. Just copied everything over from my old pc onto an external hdd then copied it over to steam. Booted Steam up and it was golden. The one thing you do need to watch out for though is that not all game saves are stored on the Steam Cloud - so be sure to check your Windows User folder for any saves to avoid losing them!