i'd go for the Isopropyl Alcohol , might wanna read this article on cleanning thermal paste
, i really cant recommend using artic silver 5 you can read at this page why http://www.arcticsilver.com/as5.htm
"Arctic Silver 5 was formulated to conduct heat, not electricity.
(While much safer than electrically conductive silver and copper greases, Arctic Silver 5 should be kept away from electrical traces, pins, and leads. While it is not electrically conductive, the compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.)"
better use arctic silver ceramique instead its 100% non-conductive and theres barlely any temperature diffrences between various thermal pastes