I'm going to go against the grain here and advocate for 165s. From the photo, it looks like your bb is pretty low, but it's hard to be sure from a pic. bb clearance isn't a top priority in road bike design, and if you've popped 700c wheels on a frame originally set up with 27" (is that the case here?), you lose a little more still. You may never encounter pedal strike, but if you do, the results can range from mildly jarring to really scary. 165s give you that extra little bit of clearance, and at least for me, the tighter radius is handy when you're really spinning. But if you find the 170mm cranks comfy, also consider narrow and/or shallow pedals as mentioned above; GR-9s or a clipless setup can give you lots of breathing room.

FWIW, I rode powergrips for a while; I can't stand them, but since I never got around to trimming them and they stuck out a bit, I could feel/hear them scape when I got close to a strike. Obviously a silly measure for long-term use, but if you really want to know for sure how close you are to striking, you could always tape a notecard or something similar to the top of the pedal and go for a spin...