I found Bridgessii come up to be the most intense. And the experience itself, to be full blown. I don't know the whole weighing thing. We normaly dose a cosmic dose. So I myself would eat like 2 - 3 feet of bridgessi. And same with pedro or any other cacti. 2 - 3 feet seems to be a visionary quest. I recommend eating same ammount of bridg, as you would eat of pedro. (If you're dosing by yourself, don't eat more than 1 - 2 feet).
Ps. Before you cook it up, chop it up, and freeze for a day or 2, let thwart, and freeze again. This way all the alkaloids will come out realy smoothly. When u defrost it, all the goo that will leak out, will be your alkaloids. DON'T LOOSE ANY. from there, a few hours of cooking and you're done.
Good Luck, if carried out correctly, it will change your life.
Love & Light :D