your mobo temp is reflective of your case temp. that is to say the air temperature in your case. this reading should be the same as the ambient air in your room or maybe even lower if you have really good airflow.
your CPU temperature should be as close to the ambient temp as possible.
in my case i have an slk 800 with a 40CFM sunon on it and a stealth 120mm fan on the side panel above it. at idle my CPU temp is 3-4C above my case temp which is equal to ambient. at full load my CPU is 7-9C higher than ambient/case temperature.
if your CPU temp is alot higher than your case temp and you have good airflow through the case than your prolly running a bit hot.