They're not that fast. A single thread build of my python/c project (pillow) takes ~ 15 seconds on a vm, ~ 30 on an ancient core duo laptop, and ... still waiting on the raspberry. edit: 5:15. So 25 times slower.
I did an analysis of Mathematica benchmarks on the Raspberry Pi and found it to be 15x slower at best and much slower when there are CPU specific optimizations:
What does that mean? What needs to warm up?