Did you look at or use either of the two links I posted? What speed is your CPU running at? The CFU utility allows you to determine and select the default speed governor. YaST allows a round about way of setting it on each restart. It is possible to run CFU on startup to select the default speed governor if you wish or you can compile your own kernel and set the default speed governor to be used by the Linux Kernel. CPU speed affects heat and thus fan speed required to cool it down.
So you indicated you solved the ATI video card problem I thought and the CPU is the next highest heat generator and power consumer. Other choices includes the motherboard chipset and hard drive, but dealing with these specially is different. For instance, allowing the hard drive to go into standby is one solution, but has a noticeable delay when allowed to startup. I am unsure of your next direction.
Also, a good cleaning of video card and CPU heat sinks, cooling fans and making sure they all work is important. Unless you pulled a new PC out of a box today or just finished cleaning it yesterday, do not discount the effect of dust build up in any PC or Laptop when heat is being a problem for you. I actually have had a Dell Laptop come up and tell me it was shutting down due to over heating once. I pulled out a can of duster spray and blasted all of the heat sinks through the vents and was amazed at the amount of dust that came out. The Laptop then fired right up as normal. I suggest you try to clean all PC’s at least once a year in normal operation.