I'm talking about this question of mine for SR4: "What are the fastest vehicles, and where or how can I get them?" - which was closed* as a duplicate of: "What is the fastest car in Saints Row 4, and where can I find it?"
In the latter question, OP asked about the fastest cars only (usually defined as a four-wheeled vehicle that runs on roads). I feel that editing that question to broaden it to include all vehicles might change too much of what OP intended with their question.
The reason I made my own question and self-answer about all vehicles is so that the answer will cover non-car vehicles too, like aircraft and motorcycles. I commented something to the same effect on the question while it was getting close votes but none of the close voters replied.
Note that the Reopen review of my question has been completed, which is one of the reasons I posted here.
* and was also ruthlessly downvoted to oblivion, but that's another topic =)