It could be because your other games are only using 1 of your 2 CPU cores, resulting in a lower CPU temperature. Check in Task Manager > Performance tab to see if both cores are being used during gameplay. You might need to go to View > CPU History > 'One graph per CPU' to see them both.
Check your temperatures and voltages with
PC Wizard during gameplay (alt-tab out of the game to see PC Wizard). Post back with a screenshot from the 'Voltage, Temperature & Fans' window. If the voltages are outside the accepted +-5% range, this could be contributing to the overheating.
How many case fans do you have, and how are they positioned? Are they all spinning, unobstructed by cables and free of dust?
Have you tried reapplying some thermal paste to the CPU?
Your PSU has 19A on each of the 3 +12V lines, enough to power 2 8600GTs. To check the rest of your components, enter your full system specs into this
power calculator and set Capacitor Aging to 25%. Click the Calculate button, then add 30% to the total to allow for PSU inefficiency.