andrewNZ: Something I don't ever see mentioned, is that faster speeds mean people get things done faster and free up connections sooner (until demand increases again).
I'd compare it to the difference between chip EFTPOS machines on dialup and broadband. The dialup ones are much slower, and so can process far fewer customers per hour.
I may totally misunderstand how these things work.
Well it would depend on how the users could utilize that speed, if they have super low caps then yes they'll free up bandwidth since they are concious of how much data they are using. If they have high caps then still yes, but at a decreased rate since they will be less concious of how much data they are spending and a more likely to use bandwidth for longer periods of time. The problem is when you give an unlimited cap and people find excuses to max out their connections for long periods of time.
Now with cell sites I believe that's less of an issue since they try to divide the bandwidth up evenly across its users.