I'm looking at Seaguar's Smackdown Tournament Braid - 15# test for Wacky-rig, weightless, shakeyhead.  I really like Sufix Performance, but they don't offer 15 # test in performance.  The 20# is tough to cast far.  I love the durability, though.  Any suggestions for a finesse braid with pound test between 15 and 20?  Anybody use 18# braid for any of those techniques?  Toray and Daiwa have it, I guess?

Is the 20 to big or small? Either way just base you're decision on diameters. I've noticed the newer braids are getting thinner with more strands. Not sure if that's good or bad. I tried a thin diameter 8 carrier and it frayed like crazy. It did cast and handle a touch better than a 4 though. I've heard the smack down is one of the smoother, tougher 8 carriers, so I may need to give it a whirl.

SX1 makes a 16lb fwiw. 

I haven't used an 8 strand yet. I just want durability and cast ability in a 15 pound test diameter range. Sx1 - have tried and had some issues on thinner 12lb test - but that could have been my fault.