The 3rd ones good for explaining ram ratio
Though on this site multiple people have told me that a ratio shouldn't be a bad thing for a amd64 for some reason. The only time I ever notice a slow down with my 5/4 ratio is when I play oblivion. But I'm not sure if thats the problem.
If your bios is like mine, it won't be displayed as a ratio but instead mhz rating 400 = 5/5, 333 = 5/4.
You would go to
Advanced>Cpu Configuration>DRAM Configuration>Max Memclock (mhz).
The guide on this site recommends the safe zone for a x2 at below 55*c though. So you might wanna just keep it how you have it now. Unless you've heard of a higher safe temp for your cpu from a reputable source.