I love cacti, they are strange plants, without leaves as we usually know them.
Well what more can I tell you about them? It is a pain in the ass to grow them if you have no patience. I have cacti grown by seed, they are 4 years old and are just one foot long. Yep thats right, that equals one dose if I would use it for entheogenic purpose. But they (and for that matter, all the plants) have already taught me a lesson and that is, patience.
If you do want to accelerate the process you have to make some grafting on faster growing cactus.
I have no experience with shrooms, but am also curious about how one can compare the two.