Which 50K are you running? I have the Wings and have run up to 50K in them.
I'll probably do the Blue Cruise, http://www.bluescruiseultra.com
, again. Last year I badly sprained/cracked my ankle 2 weeks before the race (2nd ankle injury injury in 3 months). I had it so heavily taped it was like running in a cast. It was stupid. But I had fun, albeit painful, fun!
I think I'm going to get some Wings too. Ironically, I have a pair of Wings I bought on ebay last month, but I can't wear them. They sent me two different sizes and then refunded my money and told me to keep them! That's when I bought the XA PRO 5's.