The ASIO-meter has not the same function as the performance meter (CPU).
The performance meter shows you how much CPU is being used on a certain moment. A CPU nowadays has multiple cores. Each core handles certain tasks, and the strain on each core is different for each core. (most of the times) The global (average) metering of you CPU should be more or less the same as the “average” load.
The peak meter is core-“indipendent” and shows the processing load in the realtime path of the audio engine. (i.e the audio driver) Thus: it shows the usage of the core that is being used “the most”. That is why you still have plenty of “average” cpu-load, but somewhere in that CPU, one of the cores is having trouble te keep up and reaches 100%.
The result is that the data sent to the driver does not reach the audio driver “in time” and a dropout or “pop” occurs and thus affecting performance. An overload simply means "adio packages hav not reached the driver “in time”. Nothing is burning or overloading in your system. 
What you indeed have noticed, and many of us, is something that is also well know.
On the VST Audio System page you will find the “Advanced options” section. Here you find advanced settings for the VST Engine, including a Multi Processing option. When this is activated and there is more than one CPU in your system, Steinberg states that “the processing load is distributed evenly to all available CPUs”, allowing Cubase to make full use of the combined power of the multiple processors.
Well… that is a bit of an overstatement imho, since cubase does not distribute the processing load evenly, and tends to “prefer” one single core, and thus blowing up the realtime asio-measurements.
Many people see that other software nowadays is indeed being able to do this core-handling in a more efficient way nowadays. Those programs mentioned above, but also reaper and vienna are examples of a more efficient corehandling then cubase.
I guess optimizing this in cubase is not easy also, since you will have to dive deep into the code.
But, on the other hand, is is not that bad that you can say that it is an issue. It is true that there are more efficient (evenly distributing processor load) programs available if you just take the core handling in to focus, but overall cubase is indeed multicore and still more then able to handle multiple cores
Even better is not trying to blow up your system, and learn the principles of handling cubase in an efficient way. Try to see if a freeze function can help you in avoiding reaching your system limits.
kind regards,
R.
