What will the 5 GB is going to be use for?Well since the thread is resurrected I'll post an update.
I now have the upgraded current AT&T gateway (BGW320-500) which has a fiber SFP+ module for a direct connection (no ONT) AND one of it's 4 Ethernet ports is a 5gbps port!
There is no "box" of any kind outside. The fiber runs direct from the pole to the house (aerial) and though a exterior wall to a SC-APC wall jack. Then there is a SC-APC to SC-APC fiber cable running from the wall jack to the gateway.