[alain94040]

>This analysis would suggests a 2.7× speedup vs. hash tables: 128 bytes vs. 48 bytes of memory traffic per uint64

It's ok to waste bandwidth, it doesn't directly impact performance. However, the limitation you are hitting (which directly impacts performance) is the number of memory accesses you can do (per cycle for instance) and the latency of each memory access. With linear access, after some initial read, data is ready instantly for the CPU to consume. For scattered data (hash tables), you have to pay a penalty on every read.

So the bandwidth ratio is not the right factor to look at to estimate performance.