I wouldn't even know where to begin if I were to include modern concerto. I've seen a ton of them that have harder looking orchestral parts than the piano part. For example, Christopher Rouse's piano concerto "Seeing" has a very, very difficult celesta part that often mimics the piano part note-for-note, and it has some very involved percussion parts also. That isn't an extreme example, either, for there are tons more with similar situations. As far as standard repertoire concertos go, I would say that both of the Ravel concertos have difficult orchestral parts. There are lots of individual solos that are extracted from both concertos that are used for auditions in many universities, even. Look at the trumpet part in the concerto for both hands for an example.