I would also like to add that 4 of those servers on a Dual Core machine would totally depend on the tickrate at which you are running the individual game servers at too. 33 tick would be no problem at all but if you were to start running them at 66 tick and they were all full at the same time (the same applies to 100tick) the tick rate would drop (in the netgraph).
If I may, another point to note down is that the game times you are wanting to run dont always run smoothly at 100 tick anyway. So take into consideration the mods / plugins you will be running as these can greatly affect the performance of a server.
Again if you have any problems, I'm available