Finally, I think I got how Inferno is going to play out. This quote below is from Jay Wilson interview in Australia.
So we created a fourth difficulty that we call Inferno that is ALL max-level. Max-level for a player is level 60, and so all the monsters at the start of Inferno are level 61, in Act Two they are level 62, in Three and Four they're level 63. And there are items that ONLY drop at level 61, at level 62 and so on; and they're not small number! There's a whole tier of armour in each one.
So, looking at the current item guide such as helm tier:
The last three helms (Tier 14-16) are all requiring level 60 to wear, and Tier 13 is level 59. As Jay said that there are items that ONLY drop at level 61 and so on, I think we can assume that at the end of Hell difficulty only a MAXIMUM of Tier 13 item will drop, then as follows:
Inferno Act 1 : Tier 14
Inferno Act 2 : Tier 15
Inferno Act 3 & 4: Tier 16
So, we won't ever get the chance to even see Tier 16 item before completing Act 2 Inferno. I like this to be honest, that's mean that farming for gears will be an important part of going through Inferno and people can't expect themselves to be able to clear it quickly straight after launch without doing a decent amount of farming.
Looking at the helm example above. The best helm you can get from Hell (Tier 13) will have at best 322 armor, while tier 15 helm from Act 2 Inferno can have a maximum of 397 armor, that's a 23% increase in armor.
I'll leave that up to you to think whether a 23% increase in armor a significant buff or not :P