There are some good videos of the material holding up to 70mph winds that have been posted by owners and not Kifaru (they also have some to watch as well). I also have a supertarp and had a ku pack, the material is very durable, it isn't your cheap silnylon that most tents are made out of.
I'm all in on the strength/weight ratio of the Megatarp. I'll be adding the annex with a stove to my order. The only thing I wonder about is adding a sod flap like on a wall tent. Couldn't be too much added weight and might be nice? Let's hear from some Megatarp owners if it's even been a thought or issue?