As I said, compare the specs of the specific models.
i7 is not much faster than i5 per thread.
But remember this:
There are dual core i3's which are 2 thread CPU's
There are dual core i5's which are 4 thread CPU's
There are quad core i5's that are still 4 thread CPU's
There are dual core i7's (Mini 2.7ghz BTO 2011) that are 4 thread CPU's
There are quad core i7's that are 8 thread CPU's
Now you understand why the entry quad i5 iMac does not differ much from the dual core i5 Mini, and why the quad i7 is much faster than a quad i5.
Count the threads, not the cores.
i7 is not much faster than i5 per thread.
But remember this:
There are dual core i3's which are 2 thread CPU's
There are dual core i5's which are 4 thread CPU's
There are quad core i5's that are still 4 thread CPU's
There are dual core i7's (Mini 2.7ghz BTO 2011) that are 4 thread CPU's
There are quad core i7's that are 8 thread CPU's
Now you understand why the entry quad i5 iMac does not differ much from the dual core i5 Mini, and why the quad i7 is much faster than a quad i5.
Count the threads, not the cores.