Well, my main game (55GB) took about 12 hours to download (from Amazon). Downloading from Rockstar was not happening.
The remaining 5GB patch from Rockstar for the final bits of content took about... 12 hours to download, since their servers have been boned.
Then there was a 350MB patch after that, which got to about 250MB (eventually), then eventually after various pauses and restarts I got it to 295MB, then it kept losing connection entirely and falling back to 295MB. Then eventually it completed with most of that 55MB or so downloading at about (literally) 6KB/s, so that was another hour or so for that bit.
Eventually after downloading bits of the game across 3 different days I could finally play it. Even if I had bought it boxed/retail, those last 2 bits would still have been a problem. I wasn't the only one finding Rockstar's downloader to be a POS, since there were various threads on the Rockstar forums about it as well. At least it wasn't my end.