I know I ride BMX but I recently made the switch..
I broke my cranks, and the company replaced them sending me out a pair of 170's instead of 175's because they were out of stock on the 175s for a week, and I needed to ride. (ended up mistakingly sending me a pair of 175s 2 weeks later
To me pedal clearance isnt that much of an issue as i dont really ride with my feet up and down.
I REALLY like the 170's though, 5mm of a difference isnt THAT much. Its not even 1/4th of an inch. But with the 175s I used to hit my feet with my front tire a lot. It seems the 170's don't let that happen. I learned barspins pretty much as soon as i got them.
They are only a few grams lighter, and I cannot tell a difference between the torque, and I run a pretty tall ratio for speed.
I'd say give them a whirl. You might end up finding more reason to like them.