Stop and go is defined (I guess) as just calling pre, leaving SPR < 1 behind for the flop. We then commit with flopped equity and otherwise fold. So, no donk-shoving every flop.
I just want to calculate showdown equity (to which we could later add fold equity, if available)

A similar thing often occurs in PLO, when calling a 4bet (expected to be AAxx)
to see a flop and commit on favorable flops. (I read an article once that at SPR=1 this play favors the caller even with a wide range)

Please consider the following simpler, but still real example:
BU raises, we 3bet in the BB, BU now min-4bets.
We are pretty sure that he has exactly AA.
Pot odds are 20%-25%.
Calculation for setmining is pretty easy. We flop it 12.5% of times, so we need to win one more potsized bet to break even.

But what about a hand like KQs/JTs?
We need a pretty advanced calculation to account for the different types of flops we commit on, etc.
Flopzilla shows those percentages, but fails to put it all together as equity vs AA (or range)

Do you know an easier, more convenient way to go about this?

I assume by equity you mean EV. Anyway, that’s what I will address. First I define Stop and Go as calling a pre-flop bet OOP with the intention of betting all-in on the flop no matter what cards come. It is a strategy that takes advantage of the fact that a flop hits only about 1/3 of the time.

Here is an EV equation for this situation against one opponent, where the decision point is the call of the pre-flop bet.

EV= fe*Pot + (1-fe)*(eq*(Pot +2*(Call + Bet)) - (Call+Bet))

where

Pot is pre-flop pot after villain bet
Call is hero call of villain's pre-flop bet
Bet is hero's all-in flop bet
fe is the probability villain folds to hero's flop shove
eq is hero’s win probability if villain calls the shove

One relatively easy way to work with this equation is through Excel. Using named variables is the best way but is not required. Then you can use Excel’s Goal Seek function to find the break-even value for, say, fe or eq, the value that sets EV to 0.

while this might be an actual strategy players employ, it can easily be improved on drastically by check-folding very unfavourable flops. this doesn't help in the computation at all unfortunately.

Stop and go is usually done by a short-stacker in a tournament with an above-average hand. The main idea is to get your opponent to fold since he has seen you call his pre-flop raise and then go all-in on the flop. If the flop is good, then all the better. The objective is tournament survival.

The following link has a detailed article on the strategy:

https://www.pokernews.com/strategy/1...d-go-25511.htm

Note: In the equation I posted earlier, I should have noted that the factor (Call+Bet) is equal to hero's pre-flop stack size.

Well a donk-bet is a donk-bet because you're betting when you should theoretically be checking to the stronger range, not because you bet out all the time. I feel like "stop and go" is mostly just another way to say donk-bet. You can come up with valid reasons to do it, but it usually involves trying to fold weaker "fit or fold" type players off their equity. In situations where your range is legitimately strong compared to the preflop raiser betting out is just "a lead".

That's absolutely not true. A huge mistake people make in PLO is just auto-calling 4bets with whatever they 3bet with. Plenty of suited run-down type hands are calls but random AKQx and KKxx hands are folds. Even calls though would rarely "favor" the 3bettor (as in I 3bet my rundown hoping to get 4bet). Its possibly true for deep stacks but not 100bb.

There isn't an easy way to do this but it is essentially just a math problem. It's straight implied odds as opposed to some sort of stop and go idea where we're bluffing our opponent off their equity and rely on an imprecise guess that villain will be over-folding.

You can use the HvH feature of propokertools to kind of map out how different flops look for you. Mostly with something like JTs, the graph doesn't look that much different than 55 in the sense that you're mostly whiffing and can't continue, but when you hit your equity spans a much wider range. To get a rough estimate you can just average that range. So 10% of the time we have an average of 60% equity, as opposed to 90% for a set.