Found this one, interesting test datas http://www.vpiano.net/pianosshootout1.htm
They tested 8 pianos and count their CPU usage, latency and other aspects. It is a good reference for those who played pianos in live very often.
I assume the authors don't use pianos live because that shootout misses the main point, namely: "If you had the hardware, would those pianos sound good live?"
I've got at least a grand tied up in piano samples including Ivory, The Piano, almost all the Sampletekk & PMI pianos, Truepianos and Akoustik, that have been tested in live band situations. For the most part they are great sounding pianos, but they don't work live. Ambience, box resonances, no guts to the bass and mono compatibility are regular problems. Unfortunately for my pocketbook, you can't tell whether the piano will work from the website samples, specs (layers, bits) or prestige - you HAVE to hook it up to a PA. In my initial run of tests I was using a Kurzweil PC88 (12 bit, two layer, looped pianos) in a jam situation. It was fed to the mixer along with the audio from my desktop computer. In 99% of the cases I quickly found myself going back to the PC88. The sampled pianos were certainly more real but they were also thin and didn't have the "in your face" quality of the PC88.
For those who are wondering, I'm still searching. I bounce between the Akoustik Steinway and the various Truepianos. I also have patches set up in Forte' that use the M-Audio Key Rig pianos, which kind of fit in the "it ain't love but it's not bad" category.
I really think someone needs to develop a decent live piano. Mono compatible versions, no ambience, no box resonances and controllable bass overtones so you can choose how rich (more overtones) vs ballsy (fewer overtones) a timbre you get from the wound strings. Essentially a softsynth version of a high end Yamaha / Roland piano. To put it in perspective, a teacher once described the difference between stage and reality to me. He told me you can't use real Scottish brogue on an American stage because nobody would understand you. So you use a "stage brogue" - Scottish enough to give the effect, American enough so it doesn't get in the way. In the same sense I don't need a million layers or samples because I don't need a real piano. I need a "stage piano".
And once we get the piano that works live, we can start worrying about whether it can be played with just a laptop.