A good link, thanks.
For piano especially, I found the best test is using it, because of the touch sensitivity, velocity, multi-samples and the keyboard you are using (and its feel) together. And I usually play different tempos and feels because my playing changes. I like to check different velocities to see if it is more than volume you hear as a difference (multi-samples) and play with any sensitivity settings they offer.
I am not sure it is the same for other sounds (obviously electric piano is the same, I check that out too) probably because I play a real piano also.
I presume this is the same for you and you know this I'm just adding this in for anyone else following your thread.

Let us know what you decide on