LEED EB or LEED NC?

Is there any percentage limit above which an existing building that is undergoing a renovation is considered a New Construction? The project we are working on is an existing 4 stories building of which 30% will be demolished. On the top of that, 6 more floors will be added and those will serve for commercial use. So we are trying to figure it out which LEED Rating System would be the most appropriate. Thoughts? Also, there's an intention of disassembling the prefab concrete panels from the façade and store it for sale or donation. Is there any credit other than LEED NC: MRc3 Materials Reuse and MRc2 that we should be looking at to take advantage of this practice? Thanks in advance for any comments on this issue!