I'd be really interested in seeing if you benchmarked fsync at every query vs your fsync every second policy.

My main beef with fsync every second is just that you will never, ever get a "this is what the server looked like when it went down". If the fsync at every query was only worse by a relatively small factor, and if you used write transactions for the majority of your writes (meaning fewer times needed to fsync for every query) which I'm guessing you are to protect integrity on writes, I don't see why this wouldn't be more appealing than fsync at every second?