Potato Joe :
Decends :
Im assuming you are going to SLI these 1070's so i would say it would be best to go with a second G1 so that the cards are of equal heights and you can use a HB SLI bridge. If the cards are not the same height, you will only be able to use flexible bridge reducing efficiency in the SLI. Not to mention in SLI the slower card's speed will be the speed of both cards. So might as well get ones with the same speed.
Secondary question, does the HB SLI bridge actually benefit SLI 1070s at all?
I'm using two ribbon bridges either way.
It benefits all pascal cards that are SLI Capable. It can help provide a few more FPS in 4k or higher i believe. But you are using ribbon ones so i suppose it doesn't matter. I suspect the Hybrid one would be best, putting it in top slot and the Gigabyte one below it so that way the gigabyte card isnt starved for air while breathing down the hybrid 1070's back. Not to mention the hybrid one wouldn't be nearly as starved since the main source of it's cooling is mounted away from the SLI area. But it's up to you if you want to use a hybrid card. As with all liquid cooling, there is a risk. I cannot say how long the pump and tubes would last.