I have not used any of the motherboards you`ve listed but, I have a biostar tb85 and msi z270a pro carbon. The biostar tb85 is easier to set up and is more stable than the msi z270a pro carbon. However the biostar tb85 has 6 pcie slots while the msi z270a pro carbon has 7 pcie slots, but you can use dual gpus such as amd 295x2 or an expansion card to install more than 6 gpus on the biostar tb85.
Thanks for the info but biostar motherboards are not available here and Are these
Z270 GAMING M7
Z270 GAMING M5
also like msi z270a pro carbon?
I believe they are similar, go for the z270 GAMING M5 there is a guide on bitcointalk.org on building a 7 gpu rig on it -
. In case you encounter any problems when building the rig you can refer to the link and there`ll be many people on this forum willing to help you. Also don`t purchase a intel kabylake cpu, purchase an intel celeron g3900 skylake cpu or higher.