Given the current state I've removed the comments that seem acted on, and the conversation about factoring in attack chances has been moved to chat.

I have an outstanding question though -- why are we specifically required to make an attack roll, or alternately, why was a spell that involved no attack roll unacceptable? What practical situation are we handling such that we shouldn't factor in no-attack-roll spells? Surely if we're only paying attention to one round, and you want to maximize our damage on average, and a no-attack-roll spell does the most damage, we'd want to know that, right? What am I missing? Clarifying this would be useful to answerers and voters to understand your situation.

@Pyrotechnical using a d20 you can't have 60% to hit with advantage, with "base" I meant without. I seek overall average, factoring in 0 on a miss.

The first comment on the accepted answer talks about all the 6-7 level spells that could benefit from True Strike. I just wanted to find these, but could not.

@Andras Ah, that'd help make sense out of it -- so we're seeking a great spell to capitalise upon True Strike?

@doppelgreener, yes, I thought adding this would derail this question, it seems omitting it hurt more :(

@Andras Yeah, omitting that meant we were left with weirdly specific arbitrary requirements without being told why, which also meant it was clear there was more going on we weren't being told about. In general, users don't like questions where something funny's going on like this, and it makes people uneasy about answering. (This is also the kind of situation where each new answer results in some arbitrary restriction discounting their answer without clear reason why that's bad, which you can see already happened twice, because the author didn't understand what you were going for.)

Explaining that you're trying to capitalise on True Strike would help us understand what's going on and better explain how to capitalise upon it. Instead of saying we have advantage via help, can't use metamagic, etc -- just explain we're using True Strike and that we're trying to find a reliably good spell to follow that up with, which also explains the setup limitations and the using an attack. "Reliably" explains why we're considering average damage including hit chance.

Also, you should give the With Advantage hit chance multiplier we should use, 0.84. (I'm still not convinced the hit % is necessary though. Isn't there only ever going to be the one attack roll, made with advantage? So we can just focus on pure damage output. When we multiply every answer by 0.84 to get their average overall damage, their relative damage output ranking will still be the same.)

@doppelgreener if you check the edit history, the hit chance was not there originally, someone has requested it

I am editing back and forth to keep everyone happy, this earned me a -2 downvote and a close :)

Asking "what would be good with True Strike" would be even broader and unclear: What metric, do vulnerabilities count, basically the same questions and comments would necessitate the same edits.

@András I don't suggest removing those restrictions — but remove the things you've used to simulate a true strike (you're receiving aid, might be the only one) and say you have advantage because of true strike.

So I still would have to exclude those

"you've cast true strike" instead of "assume someone is Helping you and has granted you advantage that way"

Mentioning true strike also explains how and why we're limited to one round

And it means if someone feels they can break that restriction whole offering something relevant, they can do so in an informed way that helps you.

Like "I know you said one round but if you first take a round to make sure you're upwind..." Or something.

done

now that you know my intention, feel free to edit the question, I go to sleep soon

Ok, I've cast a fifth reopen vote.