Your best bet for running one big server is using a desktop cpu. Server cpu's are made for a large number of small processes, like a web server. They have a large number of low clocked cores. Desktop cpu's are built for running games, and single big programs. They have a lower number of very highly clocked cores. Your best bet for a large single server is a overclocked 2600k with a SSD, sticking it in a 4U rackmount case, and collocating it. You also might be able to rent an overclocked desktop machine as a dedicated server, but there aren't that many hosts that offer them. I've had to do almost the same thing for large gmod servers, as source engine is almost all 1 thread.