Memory Performance, Synthetic Benchmarks
The result of going from quad-channel DDR4 to dual-channel is a 38% reduction in peak memory bandwidth. However, if the Haswell-E platform is anything like past Intel extreme platforms we shouldn't see much if any change in real-world performance.
The CPU cache performance is unchanged and this is to be expected, though the Asrock X99E-ITX/ac still showed particularly strong performance.
The X99E-ITX/ac's performance is unaffected by the reduced memory bandwidth in Cinebench R15 CPU as its performance is on par with the full-sized ATX Fatal1ty X99X Killer.
The Asrock X99E-ITX/ac scored just as well as any X99 motherboard we have tested in the past using the PCMark 7 benchmark.
Interestingly the Asrock X99E-ITX/ac scored quite a bit better than the Fatal1ty X99X Killer in the 3D Particle Movement multi-threaded test.