Actually, in that same situation, I believe it was limited by memory (MB per apache+php process), and number of processes available driven by latency. Given th

Actually, in that same situation, I believe it was limited by memory (MB per apache+php process), and number of processes available driven by latency. Given the number of processes running on a machine, and the memory that each consumed, we "couldn't use up" the processor capacity, the memory ran out first. Maybe we could have switched to something lighter, but the cost of all that development and testing would outweigh a handful of extra machines.