Hi Annie,
I have both these brands although they are a couple of years old so I forget the exact weights and specifications of them.
The 3/4 Exped Downmat is the heavier mat (about 800g???), it was pretty comfortable, pretty warm but after using it regularly for about 6 mths it started to deflate slowly. (Rather annoying!) Apparently there was a problem with the valves, because other people had the same issue.
I have been told in the shops that the newer models have a better valve. (Is that true or are the shop keepers just trying to sell their products???)
Eventually I became annoyed with it going down all the time and replaced it with one of the women's 3/4 Prolites (about 400g), which has been fine. Not quite as comfortable but roughly half the weight.
I also have a tiny Pacific Outdoors mat that weights about (280grams???) which I use in the summer, if I know I'll be sleeping on grass or sand. Not as comfy as the Prolite, but heh, very light!!!
Good luck, may your choice be comfy!!!

Melinda