Had a concert Saturday, performing Mendelssohn's Lobgesang. We were paired with another choir (larger than us), and an excellent symphony orchestra. Altogether I would guess there were at least two hundred people on stage - rather cozy and quite warm on stage, but the sound was absolutely tremendous and tremendously exciting to sing in. And Mendelssohn is a very rewarding sort of composer to sing in large choruses with, especially in a piece like this: a "hymn of praise", written to commemorate the western invention of printing - I think on one of the major anniversaries of it?
We were conducted by the conductor of the symphony orchestra (the choirs share a conductor, so there were just two conductors running around). The conductor was sort of funny and acerbic with it, the kind that really tries to get a lot out of you. I'm not sure what he's like when it's all being put together, but he kept exhorting us to get out of the music and watch the conductor. (One of the most common refrains of conductors I've known).
The parts got a bit jogged around by our choral conductor. He asked the alto 2s to help the tenors when they had to sing by themselves to open a movement, and in some parts asked the entire soprano section to sing alto to lend more power to the middle section - this, at least, is very rare. The last movement in rehearsal we basically didn't have a soprano line; those were being worked on by the other choir, who would cover for us there.
I like this rendition on youtube. There are more if you search "Mendelssohn Lobgesang" though I only have timestamps for this particular one.
( Lots and lots of talk about the piece, including time-stamps for specific parts )