Across any given system's performance spectrum, at the lower end of the scale a low cost change in configuration, like adding cache, may have a significant positive effect on performance. However, at the higher end of the scale where a system is highly tuned, it is likely it would cost a great deal more than the price of adding the cache earlier on, to achieve the same performance improvement. Thus two systems may offer similar levels of performance, but one may cost significantly more than the other. An important factor in any buying decision. The same warnings apply to analyzing pricing as performance.
Vendors can, and do, optimize configurations to minimize cost.
So the price performance, like performance, should be treated as an approximate guide, rather than a definitive figure for detailed comparisons. A good example of the importance of price is the concept of increasing performance by linking two, or more, systems together in a loosely coupled configuration. Several companies have used this technology in TPC testing to report performance above the level of their highest performing single system. The advent of TPC testing allowed vendors and users alike to abandon MIPS as a measure of relative system performance. MIPS has now been effectively replaced by the SPEC suite of tests, but like MIPS, SPEC tests are primarily a measure of processor complex performance.