Sorry for the slightly off-topic reply, but I'm fascinated by the fact that you really need 900Mbps when you're using an ISP with a 500GB/mo download cap. Why is this? At that speed, you could use up your entire monthly download cap in a little over 1 hour. How come you're so keen on massively fast download speeds that it's hard to even find a use-case for, yet don't mind relatively measly monthly download caps?
I think you've misunderstood - 500GB is not the only option they offer.
But anyhow, a good reason anyone might want a gigabit-esque connection is simply to get things done faster - if you can reduce download time, it's worth it. Absolutely the reason I buy the fastest possible connections.
It doesn't matter if you download 500GB a month or 100GB a month, if you want the things you do download delivered as fast as possible...