I searched the conference paper for "sel4" and this result seems relevant to your question: A comparison of the performance of seL4 and mC2 is not straight

I searched the conference paper for "sel4" and this result seems relevant to your question: A comparison of the performance of seL4 and mC2 is not straightforward since the verified mC2 kernel runs on a multicore x86 platform, while the verified seL4 kernel runs on ARMv6 and ARMv7 hardware and only supports single-core