On a really well lapped heatsink and chips you would probabally only get about 1c at most, on a straight out of the box combo you could get between 5-10oC depending on the processor heatsink and how ell you put it on, I know some one that got 9oC over standard thermal paste on a cel 600@900 with an FOP 32-1 and when I used it it allowed me to run at 1008mhz with my celeron 600
i got 3C degree of on my TB 1000@1236 (12*103) and Alpha pal 6035+Delta 7k and i can tell u that it really worth the money but u can buy it with a friend and cut the price by half would be nice too because the 6.5 gram is good for 25 application on CPU socket style and that it s alot of application i can say)
If you want to use all of Artic Silver’s potential, clean all the old goop off your HS and then lap it. You should read the info at Artic Silver’s Site. Think of it this way, where the thermal compound is really important is filling in the microscopic surface imperfections in the surface of the HS. You can’t get the old goop out with just solvent and a rag. If done properly, you will drop 5 to 7 degrees.