Question: Is it possible to re-use the nxt_db directory when upgrading from 0.7.4 to 0.7.5 without downloading the whole blockchain again?
Yes, it is designed to be possible to upgrade without having to delete the nxt_db directory, that's the reason I bother with applying those SQL statements.
If too slow for Raspberries, do whichever is faster, upgrade or download from scratch.
Did I manage to improve the Raspberry performance with the last release?
Does this mean that we are actually generating checkpoint files on all the nodes all the time? If so, how much work would it be to have newly installed nodes query for the most recent db files and start with that, instead of redownloading the entire blockchain. Of course, must be peer verified checksums, etc.
How fast does the DB grow at 1000TPS?