OP, we all suck. It's the nature of randonneuring to challenge us. Any rider, no matter how strong or disciplined, can be brought to tears over the course of a 600km ride. I mean think about that! Only crazy people would get on a bicycle and think "yea, I think I'm going to just keep on pedaling for 35 hours or so." Who the heck does anything for 35 hours? I can't even sit on a couch for that long.
You've received great advice and I am far too new to the sport to add to it. I can only offer my own views: see randonneuring not as a race, but as a grand adventure. You'll encounter all sorts of obstacles; vast distances, grumpy drivers, inclement weather, your own physical limits even. You're striking off into the great unknown, with nothing but your bike, some (hopefully) well chosen clothing and your muscles to propel you. Remember those two little hairy guys in the Lord of the Rings movies, they weren't racing to the volcano, they were just trudging along and doing their best to overcome whatever was placed in their way.
At your level of fitness - capable of 8 hour 200s - the time limits are meaningless to you. If you are in the right frame of mind, you will make it to the end of any ride you choose to. You just have to give up on giving up. A DNF is just not an option, what sort of story would it be if ole what's his name gave up when his little buddy was taken by the spider?!
So, in conclusion, keep your eye on the volcano, and watch for spiders.