The dollar tree foam board is pretty strong provided the paper covering stays on... The depron i think is a slight bit stiffer i built my 44" monster tensor out of 5mm depron and is a little stiffer i think seeing as it doesn't have a paper coating
foam to foam, depron is stronger. However, as Kyle stated, the paper backing makes the foamboard stronger. Depron is quite a bit lighter as well. But you will need to use spars in it to support the weight. And if you crash, depron shatters.
