Ran a 4 mile snow shoe race today. Took 4th overall. Was much better than anticipated as temp was negative 1 at start w/ wind chill at neg 15. Most of the race was on single track in the woods, so the wind chill wasn't a factor too often. Pulled the wool neck gaiter up a few times to get some warm air into the lungs, but overall a pretty fun run.
Not that my advice is worth much, but I'd say it makes a difference on the distance you are talking about. On 50K's or longer, I always use downhill's as recovery time. I am a gravity or floating the downhill kind of guy and go as fast as I can without giving much effort. The effort is based on how technical the trail is and how steep. Short steps on the uphill, length of step on downhill based on trail conditions. Any races at half marathon or shorter are just let 'er rip.
I do think core work outs, hill, and speed work strengthen the legs to get you up and down the hills without cramping or giving out.