Recommend hardware

Hi!!

first of all i want to thank the developers of such a great tool !!!

Im newbie in rig building but i want to build a nice rig. Cooling is not a trouble, cause is going to be hosted in a Datacenter, Power also is not an issue. 

My trouble making a choice of plataform is based in parts that i can get as fast as possible. 

GPU i can choose from: 

1070
http://www.evga.com/products/Product.asp...P4-6173-KR
https://www.pny.com/geforce-gtx-1070-fou...10708PB-CG

Motherboard, is there i want to ask the question: 

Gaming mother board? or server grade motherboard ? is it worth the money the diference ? Evilmoog says in a presentation that i saw in youtube that server grade is the way to go, but the $$$ impact, is it worth ? 

also, i want to buy 4 GPU's , so the next question is, a Mini 2x2 Cluster ? or a single motherboard with 4 gpus connected ? this is also that i can get relative good gaming motherboards, but server grade mother boards will take a few days to get, i want to build this RIG now!! 

is basically for use in to retrive cisco 5 passwords. I'm also willing to donate gpu time to help anybody when i'm not using the rig.