Whether you do a pan drop, suction drain through dipstick, or cooler line exchange, Sonnax engineers have found that circulating solid contaminant levels are going to sharply increase.
The key here is to make sure that an external filter of some type is installed that actually has the capability to catch these contaminants. Even something as simple as a Magnefine is a big improvement over the stock transmission filter.
Honestly, I think doing both a pan drop and a cooler line flush is a good idea. When I recently did the Mark VIII's transmission, the pan was completely disgusting, and the magnets absolutely overloaded. I will not be doing a cooler line flush again without doing a pan drop at the same time. The transmission is worth the effort.