So, regarding the witch v cultist thing. Some of it will depend on what that last ruins is, obviously. If it's, like, good or something, then you take witch for sure; if it's uh, REALLY bad, like the -2 VP thing, you are going to be more skewed to cultist. BTW, is anyone else realizing how WEIRD it will be to have the supply being somewhat unknown /aside. Anyhow, if we just assume those don't exist, or are like confusions or something, I think witch definitely wins the head-to-head. Why? In a nutshell, curses will run, ruins will run, and BAM, you're staring at a three pile ending, and hey look, those -10 VP from the curses are important, I think probably even more important than the potential chaining, with the junk getting slung around, but I could be wrong.
In general, I am less sure. I mean, they do different things. But the lab-possible effect will help engines with cultist a lot more than witch; it's just.... I mean, how good is a stack of labs anyway? It is good, don't get me wrong, but not great; well, the attack does a lot, and the trashing might, but really TFB is what you want for that. But it's nice to have a non-ambassador junking attack that works in engines a good bit better than BM! So I'm quite with chwhite here, I would guess it is somewhere in the 6-10 range for 5-costers (well, there may be more strong 5s coming here! so let's say closer to 10), but it all really depends on what that last ruins is.