Intel's Core i7 processors, packed with upto six cores, and two threads per core, provide enormous processing power for desktops that was beyond anyone's imagination even four or five years ago. But the question is do you really need such power. The answer is hell no! Most people use a computer to access facebook, check their mail and word processing. You can do all that with an Intel Pentium IV (may be even a P3) or an AMD Sempron. Heck you can do that with a smart phone.
On the other hand, some games have ridiculous minimum CPU and GPU requirements. On of the reasons for that that can be traced to relationships/partnerships between games developers and hardware vendors. Intel even paid off Dell and others to buy their lousy but expensive chips instead of AMDs cheaper but better ones. They ended up paying 1.25 billion dollars to AMD, at this rate AMD might decide that they don't need to make chips anymore. They will fire all their engineers and hire lawyers in their place, but I digress.
So the bottom line is unless you are wasting your life playing video games, by the cheapest slowest CPU on the market and that will last you a good 3 or 4 years. The cheapest CPU would be an Athlon II and it's way ahead of an i3 and even low end i5. Honestly you wouldn't be able to tell the difference between a high end i5 or a low end i5 either so and Athlon II will serve you fine. But I must admit that and i7 is heck of a lot more powerful than Athlon II or even a Phenom II X6 black edition. But I don't need such power, on the other hand I run lots of virtual machines, and an IDE, an SQL database and a webserver, often all of them at the same time. While an Athlon II can certainly handle it, a Phenom II X4 is a better bet. And's that's what I picked up on eBay the other day. To be precise it's a AMD Phenom II X4 955 3.2 black edition.
So why eBay instead of a local shop? Well most of the local shops are run by crooks and besides they don't sell AMD (in this part of the world, anti trust litigation is unheard of). The other option is to pick one up from Malaysia or Singapore but this is cheaper and I bet the quality is better too. Anyway, why am I writing this? Beause all three of my computers packed up at the same time. Two of them are now running again (albeit on life support).