Bitcoin core: boostrap.dat trade-off with "Synchronizing with network..."

Question

Being, now, aware that users of Bitcoin Core (v0.12.1.0-g9779e1e) are no longer to use a torrent download of a bootstrap.dat and, instead, are admonished to simply launch Bitcoin Core and permit "Synchronizing with network...", I nevertheless have a situation that may require a more nuanced decision:

1. I'm recovering from a backup and it says "50 weeks behind..."
2. By the time I discovered boostrap.dat was no longer faster I had already torrent downloaded most of boostrat.dat.

Number 1 leads me to believe my use case may be an exceptional use case that may download everything for the last year before becoming operational again -- rather than the minimum amount(?) necessary to begin secure operation.

Number 2 means I may be able to complete the download in about 12 hours to SATA SSD and then be able to load from that file only the minimum amount(?) necessary in a total amount of time much faster than downloading "50 weeks behind" of blockchain.

Should I go ahead with the torrent of bootstrap.dat and load it or should I stop the torrent and just let Bitcoin Core complete "Synchronizing with network..." even though it says "50 weeks behind"?

Answer 1

the minimum amount(?) necessary to begin secure operation

Letting Bitcoin Core synchronize on its own will do the following:

• Download block headers in packages of 2,000 and quickly rebuild the chain of headers for a total less than 50 MiB
• Request multiple block bodies in parallel from several peer nodes
• Validate blocks in order as they finish downloading including all transactions they contain

For the last 50 weeks that would cause Bitcoin Core to download and validate about 35 GiB of data.

Synchronizing from the bootstrap.dat you download the complete blockchain first, then rebuild the blockchain from scratch.
This means that you have to

• download more data (78 GiB instead of 35 GiB)
• have to validate blocks of more than four years instead of 50 weeks
• and delay the validation until after the download is complete instead of validating while downloading already.

It seems to me that unless the download speed from the peers is the bottleneck for you, letting Bitcoin Core synchronize on its own will be quicker. On my fairly new computer the bottleneck is the validation and not the download.