There are some sections that are relatively level where you can really get a good flow going. I just got a set of 150mm cranks yesterday and will probably install them later in the week to see how they work. That top speed was for a very short time as you can tell by looking at what the average speed was!!!
I put the 150’s on my 26x3 Muni today and went out for a quick 1 mile lap around the park, WOW!!! I cut almost 2 minutes off my usual time with the 170’s with an average of 6.7 mph and a top speed of 12.6 mph and that was only 1 mile!!!
Unfortunately, I have to ride mountain bikes with a friend who is in from out of town, so I won’t get a chance to try the 150’s in the dirt tomorrow:(