https://en.wikipedia.org/wiki/Thermal_design_power
You can make comparisons between a heat sink's TDP rating and CPU wattage, you merely have to account for the variables. For a CPU, wattage draw by the processor is equal to the heat dissipation of the processor (for engineering purposes). If a heat sink is rated for 100W TDP then it is designed to cool a processor drawing 100W full time to acceptable operating temperature (what that may be depends on the maximum allowable junction temperature as specified by the processor manufacturer typically 60-70C). For an LED drawing 100W around 50W (depending on efficiency) will be converted to heat in the case and the other 50W converted to radiant energy (which will be later converted to heat after being absorbed by surfaces in the grow room). So, you will need to remove 50W of heat from the case of the COB. Therefore, if a CPU heat sink is rated for 100W TDP cooling the processor to 60-70C then you can very safely assume that it could cool 50W of heat from the COB. However, it is good practice to build in a factor of safety to your design. A rule of thumb that I have followed is to decide what wattage you want to run the COB, multiply that by 2, and then find a CPU heat sink rated for that TDP. So... 100W x2= 200W so you could look for a CPU heat sink with a TDP rating of 200W. It's not exact, but it works for our purposes.
Please note that in my post I specified that these heat sinks are designed for active cooling with a fan. Therefore, the TDP that they are rated for is dependent on the flow rate supplied by the fan. I agree with you that increases in flow rate of the fan will most significantly impact heat dissipation. In practice for CPU coolers, active cooling at full fan speed increases heat dissipation by 3-4x over passively cooled heat sinks. Perhaps my initial post was not clear in that regard.
To the OP: those heat sinks will only come close to dissipating the heat from your COB if they are actively cooled with their fans. Don't expect to cool a COB running at more than 20W passively with those heat sinks. I know that this is outside the scope of your original question, but you'll likely need large (>140mm) pin fin heat sinks to passively cool a COB @ 100W.
