While these are certainly great little chips, the have some key differences in the chip architecture which leads on to speed and capabilities as well as the all important price!
I3 :
the i3-xxx series processor chips run on an LGA-1156 socket and have a factory clock speed of 2.4 to 3.0g Ghz, and while they are only dual core processors, they certainly still pack a punch with an L3 cache of 3-4 Mb and at the time of writing this, they are retailing on ebay for as little as $124 ,Thats is not a whole heap for a powerful little processor!

I5:

The I5 6xx and I57xx processors come in either dual or quad core and certainly pack a punch with a FSB speed of 2.5 Gt/s, an L2 cache of 256 MB and an L3 cache of 4 to 8 Mb and also run on an LGA-1156 socket.

At the time of writing, these little powerhouses are retailing on ebay for as little as $170

I7:

The i7 6xx, 7xx, 8xx and 9xx processors sit in either an LGA 1156 or 1366 socket and are all quad core. They pack a serious punch with a FSB speed of either 4.8 or 6.4 Gt/s, an L2 cache of 4×256 Mb and an L3 cache of 6-8 Mb!

At the time of writing these babies are retailing for as little as $255 on Ebay!

If you want the ultimate performance though, the I7 9xx(x) processors are 6 core powerhouses, they sit in an LGA 1366 socket with a FSB speed of 12.8 GT/s an L2 cache of 6×256 KB and an L3 cache of 12 MB these retail in excess of 2G so you are going to need to shell out for one of these, but think of the competition you are going to crush!

The New 2010 Core Processor family is shaping up to be some interesting little gadgets which have been cooked up by Intel’s engineers to bring you only the best of the latest technology in the Processor market, please see the following videos for details on what these babies can do!

all I can say is “wow, cant wait to get my hands on one of these!”