Jim,
I'm 70" tall but weigh only 130lb. and demoed the SS Speeds in CO. Diana was pondering the same question (163 or 170?) until she learned my weight. Then she recommended the 163 and it was a good choice (duh). They handled perfectly for my purposes (learning/improving PMTS movements and free skiing in frontside conditions + bumps, at least the easy bumps at Granby). I just bought a pair in that length.
Given your similar height but greater weight, the 170 would probably not be excessive. Just my $.02. I'd defer to stronger PMTS skiers/coaches, especially if they're closer to your size.
P.S. Be careful about the bindings. Mine came with PRX-12 (not from HSS), which have a higher ramp angle than most other Head bindings (7mm heel:toe delta vs. 4mm). I found that difficult to ski and painful to my knees. Diana's sold me a pair of PRD-14, which is what I demoed in CO and work much better (for me, of course).
If a higher ramp angle works for you, I have a pair of PRX-12 available... cheap to good home!