Sexstacy is not that great IMO. The sex feels a lot better, but the fact that it's near impossible to finish makes it frustrating. I like stoned-as-fuck sex muchhhh better.
Try sniffing poppers while you are fucking, it will tip you over the edge.
I can safely say after having sex many times on MDMA and weed that sex now is just as good if not better than it always has been.