I remember watching (more than a year ago) some reviews of the ultra expensive, ultra high tech Patagonia DWR down jacket.
Despite the plasma super bonded silicone treatment, and despite having a claimed fp of 1000, after a jacket came back from a medium length trip, when the jacket was held up to the light and you could see the down, it was clumping together more than it would have normally. The person doing the review compared it to another jacket, that was not DWR, and this was more lofted, less clumpy, etc.
Gives one pause for thought for the above DWR treatment, and maybe DWR treatments in general to a lesser extent.
Perhaps the best, but almost certainly least durable, down DWR, is the simple wash in wax ones? I doubt this would do any damage to the down (wax being more similar to oil than fluorocarbon, silicone, etc) . That way, if it has negative effects on the down as regards clumping, etc, the coating will degrade faster. It's also the least toxic of the treatments (well, silicone itself is pretty safe/non toxic, but i think only Patagonia was using this for a treatment).