We are currently working on a project which has a total area of about 4,000m2. The project consist of several buildings, each of them is no more than 2,300 m2. So I can work as a "Projects with Several Physically Distinct Structures".

My question is if the appropriate baseline is system 4  or system 6? 

In Accordance with Appendix G Table G3.1.1A

If my selection be in accordance of the area of each individual building we have "Nonresidential and 3 Floors or Less and <2,300 m2"  and so the answer is system 4. On the other hand, in the case that I rely to the sum of the area of the project, my selection must be system 6, as the building Type is "Nonresidential and 4 or 5 Floors and <2300 m2 or 5 Floors or Less and 2,300 m2 to 14,000 m2"