Responding to your points in reverse order!
Butterfly effect is infinite uses of one per turn, but high cost, and that doesn't really mesh with simpler forms of PC-- you need two cards, and 5+3X quanta, where X is the # of permanents you're targeting, ignoring the low atk creature's cost. It doesn't help that BE is almost never used and often considered underpowered or too niche to really be a viable option.
SoFo is a much closer analogue, with 3 permanents over 3 turns, assuming the most basic usage, and if you're making a PC spell of course you can't discount explosion(or steal, I guess), so I modeled things around those two.
The problem with a 2-cost card is that I can't make a 2-cost card
I haven't been mentioning the rulesets in my notes because I've wanted these cards to stand on their own, as if they weren't restricted. So we'll just have to settle for an increased chance, heh. Rules? What rules? Don't give me no rules, no sir!
In retrospect, 20% chance does seem to leave the target alive for far too long on average, so back up to 30 it is. Further adjustments may be implemented, like interpreting the "Gain this effect per turn" differently.
Your tables are correct. (And very pretty! Can I steal them for my notes? ^^) For the upgraded, it's important to take into account that the chance of a permanent being destroyed goes down from 51 to 20 after one is destroyed.