How can I put my CPU under very high pressure for a long period of time? Are there programs for that that I can keep running ?
Look at some distributed computing like Boinc. This runs compute intensive programs where tasks are taken and run across many machines thus allowing projects access to free computing power. In your case as the programs take up much compute power they will use the CPU heavily. Boinc runs multiple processes on your computer so will se all cores of your CPU.
Do the following once for each CPU core in your Mac, open
Terminal.app and enter the command:
The yes command will print the letter
y to standard output in an infinite loop.
Several database systems are multicore optimized. You could install something like mysql and setup a basic data set, then run some of the benchmarking tools against it. If tuned correctly, many DB systems are most efficient at high CPU load (because if it was not, you would be wasting resources).
Or, you could just wash a flash video in Safari.