If you want to see the speed as reported by cat /proc/cpuinfo increase to your CPU's rated speed, try the following. Open two terminals; in one, paste the following:
cat /dev/urandom > /dev/null
Then, in the other, check the output of cat /proc/cpuinfo again. The reported CPU speeds should have increased to the processor maximum. Kill the cat /dev/urandom process in the first terminal after you're done checking the speeds (all this command does is make the CPU usage go to 100% and output the results to the bit-bin (/dev/null)).