the DSSDs are great.... 
is it really much heavier than the SDs?

I haven't personally measured the weight on these 2 watches but a search on google provided the following info:
16600 Seadweller = 148g (Case + Bracelet)
116660 Deepsea Seadweller = 220g (Case + Bracelet)
On the wrist you'll definitely be able to feel the difference between these two timepieces because, in addition to the 70g difference in weight, the 116660 is 4mm larger in diameter and also 3mm thicker compared to the 16600.
If comfort is essential to you then the 16600 would be a better choice.
