GPU-grade memory bandwidth on low-cost FPGA solutions
I care for at least 100GB/s. On low-cost Spartan 6 FPGA this bandwidth would be success. Or it's impossible with this piece of hardware at all?


Impossible. Let's assume you're using a 512-bit memory interface, consisting of 8 memory modules in parallel. This would be very close to the maximum user I/Os on the largest available Spartan-6 part (540 user I/Os on the XC6SLX150T), and even then you might run over the limit with control signals. Even assuming this memory interface was possible, 100 GB/sec would require an I/O clock rate of ~1.5 GHz (assuming 100% efficient memory access!), which is unlikely to be attainable on a Spartan-6.

For memory-heavy applications, a GPU is often a surprisingly good solution.