I see 50ms or less TTFB, for images in the sub 200Kb range, and for videos in the 500Mb+ range, from Australia where the internet is still terrible.
I've only ever a single serve upload fail me - and it occurred when an upload hit a major global outage of infrastructure. In two years of regularly uploading 8Gb/200 files a fortnight (at the least), I've never needed custom retry logic.
And I'm not convinced it's connectivity issues, as I can SCP/FTP the same files to servers in the UK...
When I test using an actual software client (Cyberduck) to do the same thing to B2, I see pretty much the same behaviour: retries are needed, and the total upload size (due to the retries) is generally ~20% larger than the size of the files.
Felt TTFB and download speed were great too considering the massive price difference compared to s3. Though also used Cloudflare workers anyways to redirect my URLs to my b2 bucket with caching.