Just curious: do you have an orchestra you can play with? I ask because I've avoided downloading concertos because the piano is only part of the piece... and it just seems like I'd be stumped by the missing parts.
I did but a couple books of piano transcriptions of symphonies, done by Busoni, that I thought might be satisfactory in that regard, but then they really don't have "piano parts". It's been an imperfect experience, for me, at least.
Bruce