One thing to note about the Nord sample library is that all of the samples are single-layered and their dynamics can only really be controlled using a velocity controlled envelop for the amp and filter. This is different compared to something like a Montage 8 which will have quite a few multi-layered samples that have discrete samples at specific velocity levels to more closely simulate playing a guitar, for example, softly versus aggresively.
I own a Piano 4 and a Nord Grand. I enjoy both and I don't find the single-layer samples to be a problem as they impart their own creative sound to the mix.
The CP88 will not get you multi-layered samples (as far as I know). So if that's important to you, go with something like a Montage 8.