Is it better to have more cores or higher processor clock speed to decrease build time for iOS projects
Here's great article about this subject.


  More cores, slower clock speed
  
  Pros
  
  
  Applications that support multi-threading will greatly benefit from having a higher number of cores at their disposal
  Increasing the amount of cores in your CPU is a cost effective way of increasing performance
  Multi-threading support for applications will continue to improve over time
  You will be able to run more apps at once without seeing performance drops
  Great for running multiple virtual machines
  
  
  Cons
  
  
  Lower single threaded performance than a higher clock speed processor
  
  
  Fewer cores, higher clock speed
  
  Pros
  
  
  Better single threaded performance
  Lower cost option
  
  
  Cons
  
  
  Fewer cores to split between applications
  Not as strong multi-threading performance 
  


Since Xcode is able to compile sources in parallel, I'd recommend using more cores. To compile one file You don't need so much speed on one core.