Hey, CTO here.
With the wide geo-redundant storage even entire regions can be taken offline and durability is preserved. We recently had 7% of devices drop offline during the Texas power outages last month with no issues. We constantly monitor and repair the data as nodes go online and offline.
Yes, speeds do depend on users upload speeds, but we spread your files among thousands of peers. So while your 5 GB object might seem like a lot of data, each peer might only need to upload a megabyte or two. Operations are in parallel so you can get high throughput (think of lots of small straws taped together).
