There are two questions really.
The first is: what is the 5520 chipset to processor real max. speed?
Is it limited by the QPI single-link or both links may work together? (in other words, is it limited to raw 12.8GB/s or may support all four PCIe links at a time?
The second is: have Intel mesured real bandwidth used by most modern AMD/NVIDIA GPU/GPGPUs?
It's clear by their internal architecture that their theoretical max throughput may not exeed 1.25GB/s (so up to 6 GPUs may nicely share one x16 link (providing them all by switched x16 links). But is it possible to share the link between, say 8 (or even more) GPUs?
The number of PCIe lines is limited, but a fart workstation needs not only ultra-fast graphics, but ultra-fast storage too.
