PTA + Sudden Impact
The early game DPS is absolutely insane. The damage from the PTA proc is no joke—at level 3, it hits for almost 100 against enemies with 50 armor/MR. Personally, I feel like it out-damages Lethal Tempo once you hit 3 items.
The 8% increase to E's true damage from PTA is also pretty sweet.
With an auto-auto-Q-auto combo, you proc both PTA and Sudden Impact, dealing 392 damage at level 1, and a staggering 509 at level 2 including the E damage. Damn.
I'd stick with Lethal Tempo for sustained fights, but PTA is definitely worth trying if the enemy team lacks CC and is squishy.
Even just having a Recurve Bow makes the damage output ridiculous. Damn.
This was a game where I tested PTA Yi. I went Stridebreaker because of Akali and Ezreal, but even considering that, the damage was insane.
I thought about going for a crit build at first, but attack speed items actually deal more damage than I expected. Plus, there aren't really any good crit items that come with attack speed anyway. I think the best path is Blade of the Ruined King - Kraken Slayer - Terminus.