I changed from 175 to 170 on my LHT over the Summer. I much prefer the 170s. I spin more easily. With the 175s I felt too much of an on/off sensation on each revolution. I was dealing with a nagging fit issue on this bike as well. I am sort of between frame sizes and opted for the 56 over the 54. The 54 comes with 170s so I decided to try them. I am more comfortable on the bike with the shorter cranks. It was a good change for me on this particular bike, for the way this bike is ridden. I sit and spin up hills and don't get out of the saddle. I also increased my speed a bit on flats as well. YMMV but for me, it was a good change.

Many moons ago, I raced BMX with 165s.