The heart of this thread is cable modems locking up from the iCloud Photos uploader. Not slow speed during uploads. I have 150Mbps/20Mbps service, and regularly max it out with Crashplan and other cloud services. I wish people would be leaving bandwidth issues out of this thread, since it's not really the discussion.
Over the last week I've pushed up around 400GB of a 600GB library, I'm impressed with their ability to handle that kind of incoming traffic well, but that's also not the purpose of the thread. It's locking up the cable modem.
I work with many clients, with worse connections than this, and we usually will do their offsite backups over cable modem. Being small/medium businesses, they usually run their internet on the cheapest tier they can get by on, so often times 1/10th of what I'm using here and with the same model modem all around town. When doing the initial push of their backups we are almost always saturating the modem in this same manner for weeks on end until we get the initial push completed, and then smooth sailing from then on with just deltas nightly. This doesn't have the same behavior whatsoever. Nobody's cable modem locks up from that.
Could we put the speed thing to bed, and let that happen in another thread?