I agree. The drytec or other water proofing for down will not help that much with condensation.A good example of something that is waterproof is your car windshield. Condensation happens under the right conditions regardless of the material.
Down coatings are good in short term imersion and with extreme dampness. The coating will protect the down from the water. But a 6 hour sleep is enough to cause them to wet out. Synthetics are usually waterproof, too. They still condense inside. As I was saying, under the right conditions, anything will condense water on it.
Because synthetic fibers are stiffer, they will loft better. But, down is still the best choice on a per weight basis. Only when saturated with water, I mean soaked, are synthetics better. How often do you sleep in the rain? Or in a mud puddle? I am sure you choose better campsites.
Both synthetics and down loose some insulating value when damp. If you expect damp conditions where you hike, get more down, as Justin says. It will be roughly the same to carry a WM Antelope at 2#7, 5F Down bag vs. a Kelty Cosmic 35F Synthetic at 2#6. A 30F temp difference is a LOT. It will last longer and keep you warmer under every other condition. Just an example, of course.
One of the great misconceptions with condensation is that it will build up in a bag at night. This is NOT absolute and changes with humidity/heat or dew point...ie the temperature where a saturated air will condense. Generally, from about 25f and up, your body heat will change the condensation conditions in the down, lowering the dew point. Heat, along with condensation moisture, is usually forced out of a bag. Thick layers of down will allow it to condense inside, of course. Thin layers just vent it allowing the bag to stay dry. Thick bags are warmer because they hold it all in, but too warm will lead to wetter bags as the dew point moves towards your body and into the down. There was a couple articals written here that mention this, but I don't remember where...sorry. Of course, this assumes a good roof over you and no additional water added (except insensible perspiration.) You mentioned you were carefull, so, I think you can just use down.
Dampness comes in degrees. Between wet and dry there is a wide range. Sometimes, this is a disadvantage. Sometimes it is better. Down will generally vent better. You might try a lighter bag, suplimenting as needed with carried clothing. Damp down is not a problem. It will usually dry out over night making it warmer at 0200 than at 2200, when you went to bed. It will dry pretty well over the course of a night. Generally, if you are too warm, it will collapes a bit, making it cooler (from perspiration/insensible stuff causing dampness in the fill.) If it is cool, your body heat will dry it making it more lofty, hence warmer. So, it has a better comfort range than synthetics, or, even treated down. This is, perhaps, the biggest objection I have to drytec on down. It has a narrower comfort range than would otherwise be possible by artifically enhancing loft, even when damp.
Anyway, being carefull with down is always of some concern. You seem fine there. So, just get a down bag with a somewhat lower temp rating if it is always damp where you hike. Easy enough to stick a leg out, though, if you get too warm...