Akachi: I care what will the
size difference between the preload and the final release will be, since in a few days I'm going to be on a ship with a very, very slow satellite internet connection, where downloading 40GB of additional data will take 2 months and be generally frowned upon :)
If the preload is in fact not the full game, you might not even be able to start the thing without downloading the remaining data. My preload is 59 GB plus the 43 GB prerelease patch means about 100GB to download before launch day. The Day 1 patch is very likely optional and you can defer that as long as you need (assuming no gamebreaking bugs).
So anyways, with 59GB being the preload size and the game install being about 70GB on PC then I'm assuming the vast majority of the game, if not the entire thing is in the preload. Accounting for compression of the preload files and all, it looks like you won't have too much to download extra assuming you get that Day 0 patch which is likely required and not optional.
That's my guess anyway. Just keep your computer connected and Galaxy on auto-update until the last possible minute and hope for the best.