True strike says:
You extend your hand and point a finger at a target in range. Your magic grants you a brief insight into the target's defenses. On your next turn, you gain advantage on your first attack roll against the target, provided that this spell hasn't ended.
It's a concentration spell with a duration of 1 round.
Imagine I cast true strike in the first round of an encounter. Assume I have 20 in my spellcasting ability.
What spell should I use to achieve the most damage on average in one round with a spell attack roll so it benefits from true strike?
Any PC class is allowed. The focus is on spells and synergy with true strike, so ignore magic items and limited resources (like a sorcerer's metamagic) but you can use constant features (like the draconic bloodline sorcerer's Elemental Affinity).
The target does not have any resistances, vulnerabilities or immunities. The creature type is generic. There should be no setup, but we can have advantage on our first attack roll. The base hit chance is 60%.
(My best finding is inflict wounds in a 9th level slot for 50.82 damage:
11d10 * 0.6 = 60.5 * 0.6 = 50.82)