Try them both on and go with what fits. Then suck it up and just get a pair of hokas and you won't have to worry about the downhill anymore. The MT100/101/110 are basically a lightweight track shoe with an aggressive tread. I always got blisters with them on fast paced downhills. Yes they are light but they also do not provide much in the way of cushion on the downhill. I've used them for the PPA with no issues in the past but would not pick them for the PPM. The MT10 has a 4mm or so ramp and is more like a rubber sock than a shoe. You may as well just wear a pair of five fingers. Unless you have very, very good form or are a glutton for punishment, this is not a good shoe for the PPM. Sticking with the NB line, what you probably want is the (yet unreleased) MT1010. Personally I go with a standard pair of road shoes. My current shoe of choice is the Saucony Mirage. I have found that "trail" shoes provide very little benefit on barr trail.
