Hi Pork,
Yeah, I was hoping for a bit more info in here. However, I can advise that the keys are pretty much the same size as most keyboards, synths etc. I am a Piano player myself and find the keys perfectly fine for playing. I couldn't tell you if they are smaller than a standard piano but they seem okay to me and I don't find myself hitting two keys at once, which I usually do with mini keys!
Take a look at the latest Cake TV Live video on X2 and you will see Brandon Ryan playing an A-800 Pro
Gary