a Yamaha Disklavier...Someone suggested this. Anyone really know?
Please don't buy a expensive Japanese piano. (If you can afford a European piano) I had a terrible experience with it. My first piano was Yahama. (It costed as a European piano) Its timber was too light. When I had an exam on piano with a grand Seiler, f becomed mp, mp was silent.
I just bought a Seiler Upright and love it, the bass and treble sections are "exciting", not lifeless,
As a technician, I cannot argue the overall reliability of yamaha, as long as it is not a brand new small upright (not made in Japan) Yamaha uprights are the "toyota" of pianos they will get you there safely, and uneventfully, and you will get good resale, but it is no mercedes.
Your problem was one of transitioning from a familiar piano to an unfamiliar piano. Had you been practicing on a Seiler grand all year and then given a Yamaha upright in your exam, what's to say that you wouldn't have had problem executing? Your pp might have become mp, and your mp might have become f. If one were to choose a piano to optimize for exams, Yamaha might well be his best bet for the simple reason that there may well be more Yamaha uprights used in exams than just about any other brand.
What do you think about a Schimmel piano? I have a Schimmel-upright at home and really love the sound!