There's already sites and threads dedicated to card benchmarks.
Time for a thread focused entirely just on mobos supporting 6 or more cards.
Q: Any of you got any of these boards sailing successfully with 6 or more GPUs, looking for new comers as my usual mobo of choice is OOS:
asus prime b250-plus
gigabyte h170 hd3
msi z170a plus
asrock z97 anniversary
biostar z170 GT7
msi z270 pc mate