First, we'd really have to work the same beach and consider all the settings used as well as the search coil and operating frequency before we could answer your specific question. You only asked about the coil, but no clarification on the operating frequency used or other settings.
Second, I don't own a Deus, only a pair of ORX devices, so the Deus might have some adjustment functions that could make a difference .... for better or worse depending on the settings.
Third, I don't live close to a coastal beach but I will be making a saltwater beach hunt in the next few weeks to see what works for me where I go.
Fourth, I am just now working with the 9" X35 DD coil to get a handle on the strong and weak points for the places I generally hunt. When I bought my first ORX, I got it with the 5X9½ HF DD coils, and so far that is the combination [size=small](ORX w/5X9½ HF)[/size] I am enjoying the most. I did hunt a very heavy alkaline area that was pretty wet a few months back, but that device and coil handled everything just fine. Not a saltwater beach, but getting to one in the next couple of weeks.
I've been mainly using my 2nd ORX w/9" X35 coil inland, but will taker it along to analyze which seems to perform well on a salt water beach environment. Right no3, my best GUESS is the 5X9½ HF DD will come out on top, but I'll have to wait and see. It will also depend on the ground mineralization as well as the wet salt environment to deal with.
Just some thoughts,
Monte