i was going to get the thermalright HR-02 for passive cooling, but now i'm considering this scythe susanoo for passive cooling. because of the sheer size of this thing, i would guess that it might do better than the HR-02. if clearance is not an issue, then would there be any reason to go for the HR-02 instead?

If you want to do passive cooling, it is best to select a cooler designed for it. It is not just a question of find area. Also, the longer the heat tubes... the more issues you have with heat transmission. The modest looking but well proven HR-01 plus is a good pick.

This looks like it was designed for someone with the need to cool a hot graphics card.... not someone with a desire to cool without fans.

I pity your motherboard. Seriously, though, the HR-02 is more than enough on a modern CPU, maybe (only maybe) except for extreme overclocking. Plus, it's a safe bet that the TR is infinitely easier to install.

By the way, remember that a proper case is more of an issue for fanless cooling, since not many will allow you to not use system fans with impunity. Most designs have too many dead spots with just convection, and it's system fans that are closer to your ears, so worse from a silencing perspective.

It's not just size that makes a good passive cooler. Fin spacing and size is also important. A heatsink with fins packed together tightly and/or have a great depth are going to create an greater impedance on airflow. The HR-02 has fins spread farther apart and vents along the fins to help airflow enter/exit the heatsink more easily.

Looks like it is a bear to install. Here is all their CYA cautionary language:

Mandatory Factors
1. Width of the PC case must be 200mm or above (no side fan or air duct should be installed on the pc case)
2. PC case must have the screw holes for square nut in all positions to install the motherboard (in case of using motherboard spacer-free PC Case, this product cannot be installed)
*Upper and lower part of the motherboard needs to be attached with screws
*PC case must come with the square nut of its height being over 7mm
3. Supplemental power connector of the graphic card must face towards the drive (not facing towards side panel)
4. Only compatible with ATX motherboard with 9 point attachment

Conditional Factors
1. If the supplemental power connector of the graphic card is facing towards the side panel of the PC case, one of the following need to be fulfilled in order to install this product.
-distance between the position of the supplemental power connector and the PCI bracket is more than 25cm
-Expansion slot for the graphics card on the motherboard is not covered by this product.

2. Graphic card with unusual cooling devices attached (such as heat pipe) any interfere with this product. In this case, it is recommended to use the motherboard with the expansion slot not covered by this product.
*even the above factors are fulfilled the product installation is not guaranteed. Check out Scythe customer forums for additional and updated information.