175's on my bikes forever until now.
As a young roadie, a long time ago, turning over the the longer crank with a 26t cog while standing climbing just felt more natural with my tall and lanky physique.
All my mountain bikes got 175's along the way.
The 165's felt a little comical pedaling around my block when I first got them on, but out on the trail that short feeling went away in the first 20min.
165's do require a faster cadence than most of us spin. If you are a spinner (80-100rpm consistently) there is huge benefit for you. If you are a masher (60-75rpm) you are going to get used to pedaling a bit faster. I am inbetween, and most of the time it felt like I was pedaling 1/2 gear too easy or 1/2 too hard. The spin is most effective.
A oval ring is essential to the short crank. When first on the oval chainring, I noticed it layed down smoother power during climbing. The clocking of the oval combined with the faster entrance to powerstroke of the rotation magnifys this substantially.
At a smooth brisk cadence, the 165's deliver your best power output REALLY well, and noticeably quicker. Switchback's are much easier with the super quick burst of smooth power. Tech moves up ledges are easier with the same burst. And smooth cadence on sustained climbing in the saddle feels like my legs are having a good day.
The fewer pedal strikes is a nice bonus for right now, but it's just a matter of time before I get used to the new length and start clanking pedals on stuff again.
I do not have hip/knee issues, so lesser pain will not be an issue, but the lower angle of flexion is readily noticeable and I could see it helping old achey knees.
I do not ride with wattage/hrm data, so I can't give deffinitive answers as to my power output, but my rides have been on both smooth switchback climbs and slower singletrack with a lot of root step ups, and I have felt smoother/more efficient everywhere. It's not just my optomistic imagination. I rode better. Maybe not faster, but deffinitely better.
The 175mm carbon Descendant cranks weighed 480g without a chainring. The 165mm NX cranks weighed 540. I would like to get nicer cranks when they become available, but for 60g at 1/3 the price, I might put some plain black crankskins on them to cover the low budget labeling and use the money to replace my beat up old seat instead.
I drank the 165mm Kool-Aid... and it tasted pretty good