Question about DVD vs. Download for Ghosts

I had just cancelled my pre order of Battlefield 4 (It was way too similar to BF3 to warrant $60 considering I have BF3),and I moved my pre order over to Call of Duty Ghosts. I'm new to PC and I do want this game. Now... I have a 128gb Crucial M4 to put my games on, and I currently have like 60gb or so left. Ghosts calls for a 40gb install. If I get the disc version, will that install be reduced since some may be on the disc? Or does it not work that way? Curious if I should cancel the preorder and just buy it on Steam since apparently it's cheaper, and I COULD uninstall some games, but I don't want to.. If there is no difference in install size whether I get disc or download, could I move my Ghosts folder onto another harddrive while Steam is still on my M4? I have a pretty empty 1tb Caviar Black (someone's gonna yell that I should put my games on there to begin with, but eh SSD's loading times are crazy..). Someone please clarify this, thank you!

There will not be any difference in size, they both just install the game. Disk copies are just physical copies of the game, they still install the same files. I love physical copies because it feels like I actually own the game, but I get worried that I may lose them. Virtual copies just downloads them off whatever server they are hosted from, so there is no difference in the file size it will take up in your computer. I hope this helped you :)