4-Processors x 4-cores? or 8 processors x 2 cores? or 16 processors x 1 core?

Hello Nonmem Users, We running NONMEM on a DL380 with Intel 5160 3.00GHz processors (it is about 3-4 years old setver). My new 64 bit laptop runs NONMEM jobs almost as fast as this server. It seems like a good time to update the server. 4-Processors x 4-cores will run 16 simultaneous jobs; each job will have 4GB of RAM (64 GB overall). Is it better to have more processors or more cores? My best guess is that adding more cores can even decrease speed because we need one processor per job; if we use 1 processor to run 4 jobs, they will run slower than if we use one processor per job. But we are not sure. Is there any lirterature on this topic? Thanks, Pavel