theres an onza 24 muni on ebay with 165s ,also thinking of buying kh muni wheel set with the twin hole cranks already got the old kh frame with a worn out nimbus wheelset in with 150s
Until my first ride with my new setup (KH24, 137 Moments and Maguras) today I thought I was unicycling. Now I know that I am flying 
It was absolutely cool to rush through the woods. On some XC trails where I always had problems with rolling over the (big) roots, the increased speed helped a lot (you often jump over the roots just because of speed) and riding felt so natural. My speed no longer was limited by wheel wobbles but only by my ability to spin fast. On the non technical downhills I have tried I not even thought about braking with my legs and the use of the maguras felt natural too. But you have to be very careful because when you release the brake at high speeds the uni tends to roll out to the front because you have almost no leverage to control the uni. Moreover you have to be very careful when you loose momentum because then a small single root can throw you off.
More experiences will follow but the increased speed seems to be completely worth the loss of control.
Well, I might be switching back to the 150’s. I think I just need to get stronger. I hit my pedals so much today. I recovered a few times even after my foot came completely off the pedal, but I just never hit my pedals/shoes this much with my shorter cranks. I had two UPD’s and both were directly caused by pedal hits. Beautiful ride otherwise.
How are the cranks now, what size crank do you prefer now?
Well, I am still experimenting but here are the latest outcomes.
After riding a few days with the 137s I switched back to the 165s because of my ankle injury (bone bruise according to my doc). The gain in control made me feel a lot safer on the trails. Last weekend I took part at the ISDW (Innerswiss Downhill Weekend) with the long cranks and what shall I say, they are slow as hell 
For now this was the second downhill competition where I took part (I used the 165s for both) and was completely without a chance to win. For sure skill and strength are also not that good but I definitely could have gone faster with shorter cranks.
That was the reason to rethink the decision for the long cranks again and switch to the 137s last weekend after the comp. Now I am sure it only requires a lot more strength to go downhill compared to the 165s (even if I use the brake with the short cranks). But if you are aware of putting nearly the same amount of pressure on both pedals there is nearly no difference in control on downhills except the short cranks are faster and like said require more strength. I also tried a XC ride an a very narrow trail where I even had problems with the 150s and it was so much easier with the shorter cranks because of less pedal hits.
Thanks for the great response, good luck with your ankle. What crank length do you prefer for hill climbing?
For climbing I definitely prefer the longer cranks especially on rough terrain. Compared to the short cranks where you have to spin fast most of the time to climb a hill, with the long cranks you can decide wether you want to spin fast (I don’t exceed my ability to spin on (steep) uphills) or go up quite relaxed by taking advantage of the increased leverage.
I prefer the 165’s over the 150’s for muni, but that’s likely because my style is more climbing oriented with slow downhills vs high speed downhills. The terrain I ride is rooty and rocky, so I tend to ride slower, lots of rollin obstacles, so the extra length helps with control and power. I don’t have many pedal hits, but I run a 26" wheel and I’m used to the crank length. I still think 150’s are a good all around size, but I don’t think the 165’s are particularly slow, just different, I can certainly spin fast when I want to 
If you really want to see the difference, get some 137, 150, and 165’s, the ride with each for a week and see which you prefer. Sometimes it takes time to adjust…
I’m using 150’s on my 24". Right now I don’t have a brake which makes some of the longer descents a bit more work, but not bad. I think if I ever go to a 26" wheel I will go back to the 165’s. I really like them, and don’t find them too slow on the descents. I just don’t like the pedal hits when I’m riding through slots or coming around corners. After riding the same trail with both lengths I definately hit less with the 150’s.
Jerry
So I finaly got 137’s/165’s dual hole cranks which I haven’t used them much yet.
I have only very shortly used 165’s but I found that I liked them for climbing and the extra control they give on steep trails.
I havn’t riden 137’s for very long, but I do like the extra speed of the 137’s vs 150’s.
At the moment for me 137’s are not very good for climbing but if I get used to them more this may change/ better technique. Thats what I used for the unicon xc and I felt I lacked the torque needed for uphill, but maybe it was partly that I’d lost some fitness from not riding for a while cause of an injury.
I liked the 137’s for the downhill, but I wouldn’t want to use them for Northshore trails without a brake. I was surprised at what I was able to get away with 137’s and a brake, there was this steep section that I did first time on 165’s and I took two times to get with 137’s. I guess with better braking technique I could do more steep downhills with 137’s. But ATM there are some really steep downhills I can think of that I couldn’t do with 137’s that I could probably do with 165’s.
After my injury I have switched back to 150s. This seems to be the best crank length for me. 137s are fast but I like to break (partly) only with leg strength and 165s are just so slow.