On of the reasons for the 6 gig install size isn't just for the graphics. Back in 2002 Square said that the vast majority of of the game would be stored user-side- more so than the typical MMORPG. Essentially when playing Square is sending only minimal information to your computer telling it how to act and initializing preset instructions for doing just about anything they deemed common enough to pre-write. It's much more complicated than that but I think everyone gets the drift. This was done with the PS2 in mind for users who did not have access to broadband. If you experience lag when in a large group of people or with numerous spell effects going off it's much more likely that youre video card is lagging and not your connection.

This doesn't mean that serverwide lag can't exist when the pipeline reaches it's peak, but in those rare cases everyone will be effected despite their connection. Also like lionx said everyone will be downloading at 56k from them because they put a choke point on it server side. As far as I know the choke point is on downloads only and when sending informaiton you can utilize your full bandwidth (this does little good for you but gives them more leway for information spacing).

Leighton