Modem speed, how important for streaming?

Xfinity is saying I need to update my equipment to take advantage of more speed.  My current modem is rated for up to 400 mbps. My plan is around 500 and maybe it'll go higher they don't tell me how much.

Is there any benefit to increasing my speed related to streaming audio or high definition movies?  Will this improve sound quality with having a faster modem?

My modem model number is Arris sb6183 and I've had it for a long time and seems OK. My router is Netgear and that seems OK.