I despise playing outdoors. regardles of temperature. For survival, I just play time and utterly simple solos. My observation of outdoor gigs is that almost nobody listens, so why wreck yourself?
300 bpm? Like hell. In a situation like that I play in two all the way with no apologies.
Yep! Just came back from a corporate function. Thought it was inside, turns out it was outside. Sweltering humid. But what can you do. Keep time, play simple. Wipe the strings off. Keep on smiling...