The difference isn't that much (around 10% IIRC), but gigabit internet service needs a 2.5 GbE connection to your router if you want the full speed that it's capable of.
For my gigabit fiber, it's actually 1.3 Gbps (they overprovision a bit), so having 2.5G to my network is nice, in that I don't miss out on the extra 400 Mbps of bandwidth :)
For 99% of the time, though, it makes no difference. Anything over about 100 Mbps is adequate for a lot of what I do.
That's just how it works — Gigabit Ethernet doesn't mean gigabit data transfer rates. This is why all fiber providers I'm aware of provide ONTs with 2.5 GbE for their gigabit internet service.
If you're paying for gigabit internet and getting 925 Mb/sec through a gigabit Ethernet router, you're doing great. But you need to use a 2.5 GbE-capable router/switch to get advertised speeds.
