saltwater and the dh-
In my experience this means mostly estuaries and rocky coastlines, and the only setup i have used is skagit. The flies I fish and conditions I have run across require that short, heavy head that can punch thru 30mph wind while throwing big deer hair bugs, flatwings and heavy clousers.
A lot of my work in estuaries is strictly floating line and mostly shallow situations, 4-8 ft, with bass pursuing herring. to throw a big herring fly and swing it in the tide without hanging you need the floater, and you need that floater to handle big bugs. thats why I go skagit.
the rocky shores and beaches are a little different. these situations i will fish a sinktip 8-10 ft. I ran 9 ft t17 sinktip on the end of my 700 gr skagit head last year. This coupled with 9 ft leader and heavy clouser or deciever type flies gets the job done for strip retrieves.
I almost find it blasphemous to overhand my dh, its just not the way the rod is designed for its application. My experience fishing the cape flats comes from before I started using DH rods. Me and my bro have talked about this at length, but I have no doubt that I could cast skagit on the flats without disturbing these fish from the experiences I have had targeting them with the SH. When casting the dh skag style, if you are kicking up huge commotions and throwing water like a bucket, the technique probably needs work. Its a lot of grains to be chunking around but with time and practice you can do it with little commotion. Also, when that 700 grain head comes flying down into the water, you can land it with ease with just a little drop of the rod tip. Clear water or murky water, fish dont like a big splash over there head in shallow scenarios.
When I think about wade fishing flats and sand beaches as is the case down the cape, I kind of think people put to much emphasis on line speed and distance. How many times do you see someone false cast 5 times to work out 70 ft of line, only to hit the water on a backcast, lose momentum and throw a pile of spaghetti. Where if you are using the dh and a sustained anchor cast, its the same amount of work every time. Also in my surf fishing experience down the cape, blasting 90 deg from the beach probably wont yield the best results, also, unless you are in some serious waves. thigh deep with 3 footers rolling at you every 4 seconds, There should be no reason the dh cant be used with a sustained anchor cast.
This is just my look on things, certainly not meant to ruffle feathers nor do I claim to be an expert. just giving examples from things i have experienced.