XSReviews compared thermal pastes, you can read their report over here.
"Whether it’s improving airflow, upgrading a cooler or choosing the right thermal grease, everyone has a different good reason to optimize his/her system temperature. How low can you go? That’s the question I’m going to look at today, in a TIM (Thermal Interface Material) round-up. Thermal grease – or just ‘grease’ as I’ll call it from now on – is a prominent TIM in the computer industry. I’ll compare seven high-end greases to investigate where you would be best off spending on improved cooling."