Stacy, I would stick with the schedule 40. We've installed a lot of them - all Sch 40 with the glued joints. Never had a problem with them. It's really easy. Just be sure to clean and prime the pipe ends prior to applying the glue.
About the SDR pipe, I've not run through the calculations myself, but you should be able to calculate the pressure in a siphon by using Bernoulli's equation. Once you get that pressure, compare it to the pressure rating of the SDR pipe. That will tell you for sure.
