I did a bunch of testing with ARM (ThunderX) for an IPC workload using this codebase: github.com/sargun/wat. Unfortunately, it no longer runs on ARM, because I'm using inline assembly.

The ThunderX's power comes from the fact it's a 48-core CPU, which is awesome for web workloads. The problem comes in that inter-core transfer is ridiculously slow. To make a 64-byte RPC (return / response), was in the area of ~1100 nanoseconds, whereas x86-64 was on the order of 500 nanoseconds on a 2 generation old CPU. Testing on a more modern CPU cut the time further.

I'd love to see ARM either catch-up in single-core performance, or multi-core performance, but until then I don't feel like it's viable.