It's a machine with 378 GiB of RAM and 64 threads running Scientific Linux 7.2, that we use mainly for benchmarks.
Building the index was really all about memory because the CPUs have actually a lower per-thread performance (2.30 GHz vs 3.5 GHz) compared to those of my regular workstation, which was unable to build it.
If your regular workstation was using more CPU, I guess it was because of swapping. Thanks for the statistics, it means a "commodity" CPU could handle this fine, the bottleneck is RAM. I wonder how expensive it is to buy a machine like yours... it sounds like in the $30K-$50K range?
You're right. The limited query language of hdtSearch is closer to grep than to SPARQL.
Thank you for pointing out Fuseki, I'll have a look at it.
I think a SPARQL command-line tool could exist, but AFAICT it doesn't exist (yet?). Anyway, I have already successfully setup Fuseki with a HDT backend, although my HDT files are all small. Feel free to drop me an email if you need any help setting up Fuseki.