Two of my three Londons were uncomfortably warm, Connemarathon was in the early 20's C, Cape Town finished at +30 C. I'm no fan of the heat and I'm glad not have run London or Brighton this year as both looked roasting to me. That said I am revising my (silent) vow not to endure another City marathon in light of the walk/run revelations above. In fact I'm thinking of a serious PB attempt next year, possibly at Brighton, using precisely this strategy.
You know, I really wish I hadn't said that out loud ...