The difference between the XiR-2300 and XiR-3500 is in the cooling fins on top. Here you can see that the 3500 has copper fins where the heat is dumped into the air inside of the case.
On the side we see the fins and how thin they are. Note the aluminium heatsink on the bottom, just above the heatpipes.
If you have seen one side you have seen them all.
Here we see the aluminium heatsink that rests above the fins. When the air passes through the fin area it blows on these fins and aids in cooling the processor.
On top we found the same fan used on the XiR-2300. The fan lights up with two orange LEDs and is recessed inside of the copper.
I found the wire for the XiR-3500 to be long enough to connect to any of the motherboard fan headers if needed. Since all boards keep the CPU fan header close to the CPU, Nexus has included a small piece of heat shrink tubing so you can tuck the extra wire away.
The business side of the heatsink looks just as good as everything we have seen so far. The cooler has a mirror finish and will make very good contact with the CPU.