I’m doing the SLMM this year too and have just bought (2 weeks ago) a pair of Mizuna trail shoes (can’t remember the model name). They fit like my road shoes and feel like a pair of (very fast and grippy) slippers, lovely 🙂
Ran the SLMM in 2011 in a pair of Inov8 Terrocs and found that whilst they gripped very well the soles were too flexible and my feet were in agony for about a week afterwards.
Whatever you choose, do NOT get goretex uppers. your feet will get wet anyway and ypu’re much better having shoes that’ll let the wet out quickly rather than hold it in (IMO & IME)
As tragically1969 says (sort of), fit is everything