The thing is, you're kind of comparing apples to oranges. Each extra ounce of performance doesn't really have the same value or ability to percieve such performance (and different CPUs in some cases have different features that go beyond simply processing more instructions per second). If the specs of your hardware exceeds what is necessary for optimal performance of the software you're running. I frankly consider the price/performance ratio to be a dubious statistic. all it is is the price over instructions per second, and that value alone is not enough to assess the worth of the CPU.It doesn't change the fact that you have paid for a CPU that have a worse performance/price ratio (and overclocking potential) than its Intel counterparts :s
If you don't need the latest i5/i7, why pay for it? The mainstream AMD CPU is cheaper and will work just as well for most people in most situations. Only if you're a really hardcore user does most of this even matter. Even if you buy the more expensive or better "price/performance ratio" CPU, you're still going to replace it just as / nearly as often, so are you really saving money? Answer: Probably not.