Speed of Cache Memory

Between 25MHz and 5GHz - it depends on the CPU

Often moden CPU's it's linked to the speed of the CPU (ie 3GHz Core 2 has 3GHz cache)... But the latest CPU's with level 3 cache have this running at a lower speed, but level 1 and 2 at full speed...

Such an open ended question - do you have a specific CPU in mind

Of what?  

Which cache? The new i7 has L1,L2, and L3 cache in the chip. Each running level running slower than the previous.

Use Memtest86+, this will report your speed of main RAM, and L1 and L2 cache.

A system info/benchmarking/testing tool called Everest can tell you too

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