I came across a sweet article on how Apple can tell if their new iPhone is “good enough” and had to link to it. The piece also had a great set of charts showing the iPhone performance metrics by iPhone version/generation, which I’m sharing below:
I highly recommend you read the article; it’s really really interesting. Some of the comments are good too.

September 24th, 2012 at 5:09 am
Hi Healy,
Unlike what I’ve written on your former article (http://www.startable.com/2012/09/17/these-new-smartphones-are-fast/) those changes are nice for the statistics. But 98% of the users don’t care.
What really matters for the user is usability, and user expercience f.e., more than technology.
September 24th, 2012 at 4:27 pm
I think consumers DO care, but not in terms of the speed stats – they care because they are using processing heavy apps on their phones. Thinks like games, mobile scanning (in my company’s case) – some of these apps require lots of compute power.
So it’s app makers who should care about the increasing speed of the phones, and the end users will gladly use whatever their phone can handle.