I've run experiments/developed on both Applied Micro's X-Gene 1 and Cavium's ThunderX (the original). Both of these have been touted as "ARM servers". The X-Gene was complete crap in terms of both performance and power consumption. The ThunderX was only really useful for highly-parallel applications that don't require a lot of horsepower, and even then it's a power hog. I'm cautiously optimistic with Qualcomm's Centr…
In the conclusion they mention: "The largest win by far for Falkor is the low power consumption." (Falkor is the name of Qualcomm's Core).