No shelf life I am aware of. Over time the "silver" particles settle out somewhat leaving a clear fluid. Very little, if any, temp difference between AS3 and AS5.
I used AS3 on my [email protected] with stock cooler and it was awesome idle was 27C load 41C. AS5 is 26C and load 39C I didnt get a huge diffence but I bought it so I could get that little extra bit of cooling. I also lapped this heatsink . I think im getting all I can get out of this little heatsink. If I had like a SP-94 the temp might drop more because that cooler is better then the stock heat sink. I think these are good temps with this stock cooler. But my 2 30 cfm fan, vantec tornado 80mm full speed(have to turn off alot cause its fricken loud....) thermaltake Smart Fan full speed and my 120mm fan that runs on 120volt flowing like 130cfm<---pretty quiet... helps those temps.
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