I used Arctic Silver 5 and after re-installation, the CPU temps dropped by 6 to 8 degrees F. This drop in temps was achieved by polishing the base of the heatsink and leaving the CPU alone (no polishing). When cleaning the heat spreader portion of the CPU, use an alcohol swab and hold the CPU upside-down. This will prevent alcohol from migrating into the CPU and causing problems. Alcohol swabs are available at most pharmacies.
Apply three 1mm beads (balls) of AS5 more towards the center of the CPU because the center is dished inwards (concave). Now use a thin 1/2 mil (0.0005" thick) sandwich bag wrapped around your finger, place the CPU on a clean sheet of paper and work the AS5 all around the CPU. Securely hold the CPU with your other hand while doing this. Remember, the CPU surface is dished.
Here is a guide written by me, for polishing (erroneously referred to as lapping) the base of the heatsink:
Guide to Polishing Heatsink bases.
Polishing Heatsink bases is usually done by enthusiasts in order to improve heat transfer between the CPU and the heatsink. This, when done correctly results in lower CPU temps, thereby prolonging CPU life and also improving Overclocking capabilities.
Polishing is loosely referred to as "Lapping", but let it be known that whereas Polishing can be done at home on a flat work surface, Lapping can only be done utilizing highly accurate, expensive, and precise Lapping Machines.
Flatness and an improvement in micro finish is the objective, not necessarily a mirror finish. Frequently, after polishing, the improved flatness and the fine micro finish will make the surface look more or less like a mirror finish.
Tools requited are 1200 grit Silicon Carbide (wet or dry) paper, 2000 grit Silicon Carbide (wet or dry) paper (optional), elbow grease, and a few drops of water.
Here are the series of steps for polishing the base of a heatsink:
1. Find a flat surface to use as a base. A piece of 12" x 12" x 1/4" glass will work (glass top cocktail table, end table, breakfast table).
2. Lay a full sheet of 1200 grit Silicon Carbide paper flat on the glass surface and ensure that this sheet does not slip or slide during the polishing process. Put about 4 drops of water in the center of this sheet.
3. Place the heatsink base squarely over the center of the Silicon Carbide paper and gently start moving the heatsink base back and forth in about 2" strokes. The direction of the stroking must be towards you and away from you. Care must be taken not to tip the heatsink while you are doing this. Use a light downward force. Light force. Light force. Holding the heatsink closer to the base will help. Again, light downward force. (Practice doing this on a sheet of plain paper first if necessary - this will give you confidence).
4. Continue the stroking towards you and away from you, staying on the same central area of the Silicon Carbide sheet. Move your body (not the work piece) about 30 degrees and continue the stroking. Like dancing around a May pole. This will change the polishing direction on the heatsink base. Repeat for about 10 minutes.
5. By now, you will notice that the polishing residue on the Silicon Carbide paper is reddish - this is the color of the copper base under the Nickel plating film that is now polished away. Using the edge of a razor blade is an approximation of a straight edge. It is not a straight edge, but will give you ball park information that is close enough.
6. Continue for 10 more minutes on the same sheet of Silicon Carbide paper, and you are done. VIOLA!
7. Continuing Polishing with the 2000 grit paper is purely optional. Like icing (frosting) on the cake.
A note about the CPU: Leave the CPU alone. The heat spreader of the CPU is a sheet metal component made by the draw (see "deep drawing" ) process. The thermal expansion characteristics of thin sheet metal drawn parts are hard to determine. I am reasonably sure (oxymoron?) that there will be some improvement in heat transfer if the high spots at the corners of the CPU are polished away, but the marginal gains may not be worth the efforts. Therefore, I am not recommending any polishing of the CPU. Another point to note would be that any alteration will void the warranty.