I would not use something you have not used on a long ride for an event like that. So ditto what jobob said about sticking with what you have been training with.

I have been using SE mixed with Power Bar's endurance drink. Works very well. I have used it in long rides, but my nemesis is generally heat and altitude, so we'll see how it works Saturday. I've not tried Perpetuem.

I have eaten other things with the SE - cokes, for example. I don't want as much food with the SE as I would without, but what I do eat doesn't see m to interact badly. I was also a little put off by those warnings, but in practice, it seems okay.