I've been last back on every ride I've done bar 1. On one of these rides at one of the intermediate controls I said to the organiser "I'll try not to make you wait too long". He replied "Don't worry about it, take what time you need, just be safe". It made me realise that organisers have committed to sticking around for the full time limit, and I shouldn't worry, or over do it to get back earlier if I can't. Sure it's great if we're all round a 200 in under 10 hours and the org can get to the pub, but the reality is we all trickle in over about 6 hours and they are fine with that.
Perhaps my view would be different if I was doing events that are more than what AUK considers X rated.
On a recent 300, I took over 19 hours total time (grrrr head winds). The main finish was a bar that closed at 0000, and so the finish moved to the organisers house. I had expected that arriving I'd find a sleepy org wanting to goto bed, that I'd just hand them my card and be on my way. Instead they invited me in, warmed me up with hot soup and drink (it had got cold and wet in the last 2 hours). We chatted, and the org was really friendly and put me at ease about taking so long.
What I have started doing tho, is I carry an iridium tracker (think spot, but made by Garmin). It relays my position every 10 minutes by satellite to a web page, I try to remember to give organisers login info for this tracker, that way they can see, yes this rider is alive, yes they are nearly here, I'll put the kettle on.
Good luck, and ride safe!
J