Thankfully a competitor offers true gigabit for about the same price, and so that’s what I subscribe to.
Where I live we mostly have symmetrical ethernet fiber, and some cable. We started using fiber long before PON came out and it never became popular here so pretty much all fiber here is 100/100, 1000/1000 or even 10000/10000.
However, you only need to send an ACK when the TCP window is full, not for every incoming packet. If the TCP window is set at 64k, for example, and assuming an MSS of 1460, then you can receive a total of ~66K bytes for each ACK you send ((64k/1460)*1500, assuming the provider counts every byte in every packet, not just the TCP payload). The window size can actually scale much higher though, up to 1GB. So, in principle, yes, you can comfortably get this much download speed with only this much upload speed.
Of course, this would only apply for downloading huge files with a very efficient implementation. If you are using HTTP to download lots of small resources, your uplink would be saturated with GETs far before you saturate your downlink.
Other than than that, totally great
1.2Gbps downstream is enough for >50 such 4k video streams without saturation -- something that will probably never happen in any household, even in Grandma's house on Christmas Eve with a bunch of grandkids around.
Meanwhile, I've had single-player games of Factorio of medium complexity that would saturate 20Mbps upstream.
Nobody needs a connection that is so heavily lopsided as 1.2Gbps/20Mbps is except for the marketing department, and the DOCSIS sunk-cost-fallacy department.
I was using Factorio, as a single player, with the thing split into two parts: A server component, and a client component.
The data betwixt my headless server and my client was just getting too heavy at times for the 20Mbps upstream of that server.
Why so much data? Thousands of bots, constant wars, lots of things being moved around, interplanetary mining happening on a decent scale... The data transferred gets bigger as the game becomes more complex.
"But, like -- why didn't you just play it remotely like everyone else does using Steam's remote play or something?"
The latency of Remote Play sucks in ways that are distracting to me. The h.264 video sucks and has artifacts, presumably because of tradeoffs made to improve latency. My 10Mbps upstream at home works OK with Plex and hardware encoding where latency isn't important, but it doesn't work well at all for me with Factorio.
Splitting Factorio into two parts (client and server) eliminates video encoding, but it isn't completely without cost.
"But you said you had a server with a 20Mbps connection. What happened to that?"
I do. But it's under my desk at work (as is tradition), not at home. And that box doesn't have enough GPU oomph to deal with rendering Factorio.
"Right. OK, weirdo. So why aren't you just playing Factorio at home on your presumed gaming PC, then?"
Sometimes, I'm not at home or I just don't want to sit at my desk. My laptop has enough GPU to run Factorio smoothly as a client, but it does not have enough CPU to keep a moderately-complex game running smoothly on its own. And that's where splitting the game into two parts becomes worthwhile for me.
(Or, you know: Maybe I just want to play it online with a friend, like a normal person might -- but someone still has to run the server, somewhere. Some options include running that server on available hardware with available connections [for "free"], or renting hardware from Hetzner or something [not even a little bit free].
The point is: I've found that it sucks running a Factorio server with a 20Mbps upstream, even with just a single player, and thus a top-flight residential Comcast connection won't keep up. If I had 5 friends who wanted to play instead of 0 friends, that problem would be even more pronounced.
I mean. It's 2024, my dudes. What's up with this 60:1 down:up ratio?)
Silliness aside, it's a built-in part of "Multiplayer," which is included with the base game. But my late-night brain refused to use the word "Multiplayer" in an instance where only a single player (me) has ever been involved.
Like Quake was back in the day, online/multiplayer play of Factorio requires servers, and those servers are all run by regular-ish people. Some servers are public and are easy to find (and as with Quake, sometimes this is unintentional), and some [like my own] are private, unlisted, and don't even exist on the public Internet.
Aggressively compressed 4K, it's convenient for them to have convinced everyone that resolution is the one measure of video quality.
4K content on blu-ray UHD is H265 at 72, 92, 123, or 144 Mbps.
It would be a lot more data than Netflix will send you, but still doesn't saturate a fiber connection.