It may mean that the fan on the heatsink is running out of lub or dying.
I have to assume that you are monitoring temperatures when running benchmarks.
You aren't getting it.
There is no such thing as a consensus on the "cut-off" for a "reasonable" score. The score (obviously) doesn't decrease over time (unless the CPU is throttling from temperature). You can compare it to the score of the latest generation of CPU, but those numbers are up to the individual user to interpret. Some people feel even 5% is worth paying a difference, because they can afford to chase every new generation of hardware. Others hold for 10%, or 20%, or whatever number of years they are comfortable with before renewing their system. There are still people hanging on to Core 2 or even Nehalems, because they don't need anything better. Different people, different resource requirements, different decisions. For most people, those benchmark numbers mean nothing. Benchmark numbers matter to overclocking enthusiasts because they push their system for sake of pushing the limits, or for some, merely a case of epeen. For all the hardware enthusiast forums I visit, I have never seen anyone use the raw benchmark scores to decide on an upgrade.
We are long past the stage where every iteration is capable of yielding even faster boot times. Now the CPU isn't bottlenecking anywhere except for the most cutting edge games, especially single-threaded games.
The benchmark that truly matter is still the software that you run every day.
Finally, if you have been reading hardware reviews, you should know that different benchmarking software will give somewhat different results, because they test the system slightly differently. Furthermore, systems can be benchmarked with more than dedicated software like PCMark, Unigene, etc. Even normal applications like Winrar, Handbrake, Linpack, etc, can be used to measure system performance in multiple ways.