Some people will argue that it is once you give it roughly 200 hours on a good amount of load that it is still up near the top. Honestly, I would go with something different now a days. Shin etsu, gelid extreme, mx-3, or ocz freeze will be your best options. Just choose one that fits your needs
I use gelid extreme and I love it. It is very easy to apply and works extremely well.
plus ic7 diamond and coollaboratory's liquid metal pro/ultra