the only prob with ac5 would be the use of 99.7-99.8% of micronised silver. Silver being a metal in nature if not careful can cause electrical conductivity and more worst short circuits due to virtual connections on the board.... also that because it liquifies, it has a problem with detoriation over time. Given by a website i read somewhere, you would only appreciate the intrinsic capabilities of ac5 when you are an overclocker because of the heat transfer capability. Otherwise any other paste would do, like ceramique:)