Is it better to have more cores or higher processor clock speed to decrease build time for iOS projects

Solution 1:

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.

Solution 2:

Something to consider here is that software builds are often I/O intensive rather than CPU intensive. Increasing disk speed or bus speed would help a bit here, but probably not significantly. The details, of course, would depend on the details of your project. Because disk I/O would be the bottleneck, I'm not sure if the distinction between higher clock speeds or more cores would be at all significant.