Delta 400 is a little 'awkward' in the highlights; not sure how to exactly put my finger on it. If you use the film at EI 200 instead of its ISO rating of 400, all you do is push the entire tone curve up toward those awkward highlights.
To try to explain; even when using compensating style development, by slowing down agitation, which compresses the highlights, and shot at box speed, I often find myself burning a lot of highlights with Delta 400. I have not had that happen with Delta 100, which has highlights that seem to have a very linear response to exposure. In the right hands I'm sure Delta 400 is just fabulous and gives amazing results; all I'm saying is I'm having a bit of a hard time with it. I've used it with Rodinal, DK50, and replenished Xtol. Even after adjusting for high contrast by shortening the development time appropriately, and slowing down agitation, I just don't like how the highlights print. It could be a matter of taste, but it's as though there is a normal tone scale until I get to the very brightest highlights, and they block up.
If I were you I think I would start using it at its rated speed. Then, after your trip, purchase another roll of Delta 400 and shoot that at 400 as well. Then develop your test roll first, to see if you need to make any adjustments before you develop your important film. Good luck!
Thanks very much. I'd heard similar things about the highlights. Box speed it is then.