There is always something better, but usually there are differences of a few degrees Celsius. You may have applied too much or too little thermal paste. The cooler is not mounted correctly. The cooling/ventilation in the case is not optimal. The fans on the radiator are not turned up to full power. Also note that it is summer and the room temperature has a direct influence on the overall temperature.
According to my information, the following thermal pastes are better:
Better than Arctic 5:
GELID GC Extreme (3.50g, 8.50W/m K)
Better than Gelid Extreme:
Thermal Grizzly Kryonaut (1g, 12.50W/m K)
On the internet you can find an incredible amount of information on this, comparison of thermal pastes and temperatures, why is the temp too high for my CPU, etc.
You might be interested in the following article:
http://www.overclock.net/t...