I find your topic interesting in that I am going from a Yamaha C-3 to a Steinway Model L. I love my C-3, that I have had for 6 years, but I have recently gotton much more serious and have decided to take the plunge....and buy the Steinway.
My reason for the change is the tone...and I had to play a lot of Steinways before I found one that I liked....including a number of Model B's that I really found distasteful to my ears.
But there is No Question that the Yamaha is more stable, and, for what you get, a better "quality" piano from the factory. In fact, if I didn't live in the New York area, where I can get a factory technician to my house, I probably wouldn't get the Steinway. I hope to change that opinion in a year, but that's how I feel right now.