The Turbo config for the i5 520M is 2/4, every number indicates a 133mhz clock speed increase.
So this means when 2 cores are active, the maximum speed of the CPU is 2400Mhz+(2*133)266Mhz=2.67Ghz;
and when only 1 core is active, the maximum speed become 2400mhz+(4*133)533Mhz=2.93Ghz.
This works the same for the i7-720QM, its Turbo config being 1/1/6/9.
So When 3 or 4 cores are active, the max clock speed is 1600Mhz+133Mhz=1.73Ghz,
when only 2 cores are active it become 1600Mhz+(6*133)800Mhz=2.4Ghz;
and when only 1 core is active it becomes 1600Mhz+(9*133)1200Mhz=2.8Ghz
You can find the Turbo configs on Wikipedia: http://en.wikipedia.org/wiki/List_of_Intel_Core_i7_microprocessors