Running the benchmark with SwiftyJSON 3.1.4 (currently the latest) shows a 25% perf gain with JASON, on-device with a 5C.
Just wanted to make a note for others who might be searching for on-device benchmarks, feel free to close the issue.
Related: the following test case shows a 15x speed improvement with JASON over SwiftyJSON in what I have found to be the most frequent bottleneck in my projects (large NSDictionary data objects):
#42