I just built a rig tonight with that motherboard and a G4400... it mines with 6 1080ti cards just fine. I would think the G3900 would be fine too.
Thanks alot i can go with the G4400 to about the same price you have 6 GPU's running on that?
Yes, I put six of the nvidia 1080ti GPUs on the mobo. It's mining very well right now. I've built two other rigs with different motherboards, and the G4400 works with six cards on them with minimal issue as well.
The G4400 and the G3900 are virtually identical, the only difference being the 4400 has a bit more clock speed, a little bit more cache, and only uses 2-3 more watts than the 3900. It's not that you'll need the clock speed or cache... my G4400 runs at 8 to 18% load mining with six 1080ti GPUs.