Unless the Yamaha is in total disrepair, I can't imagine using the Steinway.I disagree about the non-issues in another post, though. It makes a big difference to have a new action in the Steinway, especially if it is not an Steinway action (i.e., Renner). Hammer quality can vary very greatly, let alone voicing. Also, unless it has been rebuilt, I seriously doubt that the 1936 piano is in playable condition.Big repertoire; I would assume you make this decision yourself, although I did once see a total knucklehead try to play a tiny Steinway L when there was a Bechstein C available in in perfect repair. Do what you think is right.
Alde,I wish you success with your concert.Do come back and let us know how it goes after your performance.