LIke so many situations, the answer is, "It depends." Are you planning to record via mics, or via line-in from some outboard pre-amp, or direct from the concert PA system?
I've found the PMD670 to be a great alternative to cassette tape, DAT, and minidisc for nature recording using a Telinga mic and parabola. It's reliable in severe tropical conditions, and the results sound great.
That said, I'm very interested in the Fostex FR-2 (with Oade mods, perhaps) and in the Sound Devices 722 (if it ever ships).
Flintstone