the elemental belts and gorgets are best for most the merit weaponskills. this is true of shijin spiral as well. This is because the tp modifier works on each hit.
Actually, TP modifier is not replicated on all hits on Shijin Spiral (like it is on many of the multihit merit WS - see this list
). Therefore, Gorget/Belt help SS less than they help many of the WS.
That being said, it's STILL a good choice for SS. Other good options would include Agasaya, Rancor Collar (if you aren't using mantle), and Faith.
For belt, Artful/+1 is probably the best choice for SS. Anguinus and Elemental belts are solid options too.