Personal preference for me is Arctic MX-2, costs way cheaper for me all the time at my local computer store. Only 4.99 for 4grams of MX-2 while Silver 5 costs 19.99
Anyways as you can see the MX-4 and MX-2 which are both non-conductive beat the silver 5.http://skinneelabs.com/2011-thermal-paste-review-comparison/2/
That being said grab either MX-2 or MX-4 depending on the price. The benchmarks only show a very small difference between the two (around 0.5 of a degree).