The picture above shows exactly how either heatsink will fit an AMD XP cpu, now you know why the spacers are included. I first tried without them and had no troubles, but they are included for your benefit so I suggest you do use them since it does help to lessen the chance of a chipped core.

The above picture shows the bottom of both heatsinks so you see how they compare. The SLK800 is of course the larger heatsink. Now this is where it gets interesting. The SLK800 is suppose to fit either a 60mm, 70mm or 80mm fan and it does so easily thanks to the 4 holes on each side (see first pic below) where the clips fit in, the various holes are far the various size fans. This means you can use various sizes of 60, 70 and 80mm fans, 15mm to 38mm thick. The SLK600 has 3 holes on each side to fit either a 25mm or 38mm 60mm fan. As you can see on the picture to the right it has 3 holes, but 2 are specifically made for fans, thoughThermalright doesn't count the middle hole but the clips do fit just fine in them. All these great fan options make both of these heatsinks very versatile. Something I don't think we've seen before.

These are all solid copper heatsinks with the fins soldered to the heatplate. Now notice in the pictures below, notice that "U" shape in the middle, where the clip fits through. That goes all the way through each heatsink and is a solid chunk of copper which is also the bottom heatplate. That part absorbs most of the heat while the fins with help from the airflow from the fan help dissipate the heat.

Ok, now more about how various fans can fit on these heatsinks. As mentioned before the SLK800 fits either a 60, 70 or 80mm fan while the SLK600 fits a 60mm fan, but various sized ones. Your mileage may vary since some fans are designed differently but I fit a 92mm fan on the SLK800 (see first pic below) and a 80mm fan on the SLK600. I have 3 different 80mm fans here and each fit on the SLK600. Though not exactly a perfect fit and a bit off center, at least they fit and worked. See pic on the right. Those extra holes on the sides of each heatsink come in very handy. Larger fan = better and quieter airflow and even more cooling for components nearby. Again though, your mileage may vary depending on the fan design, naturally.