On disc space:
Many PS3 games re-use the same data on each level due to slow read times from the blu ray drive. Resistence is a good example, that game could have fit on a DL-DVD. I don't know if MGS 4 does this or not, but even with a 4.6GB install there's a good chance.
On sales:
Following GTA IV is going to be tough, especially if reviewers mark it anything less than GOTY.
Predicting 2 million lifetime.









