I used orbit with rapidshare, megaupload and mediafire.. i got about 200kbps which is the highest possible with my connection.. so, i see no reason to believe otherwise..
No way it's gonna differ unless you have a little space left in the drive in which you have OS and the game.
and also, if it's a lightweight game, that is also not applicable..
If you have any doubt with mind about the data in C drive going deleted, just grab a Linux live cd, boot from it, save the important files and then repair or reformat..