I put it at 5, where 6 is 2014 5e, and 9 is A5e. I would put 1e at 6 as well, 2e at 7, 3e at 5, and 4e at 3. For reference, DCC and Shadowdark are both at 7, and the various Without Number games and ACKS are all at 8. That's it for games I consider to be a kind of "D&D" with which I am familiar...