Thats a good squat Josh. Try a 1RM, I promise it wont kill you.
We use a 42cm bench, 33 cm box, 29cm box and have gone down to 15cm box, my wife Nina squatted 70kg to 15cm blocks.
We use the 42cm bench for overload, then we work down, the 29cm box is well below parallel, and a legal squat at PTC.
Double bodyweight squats are a great effort, and what I consider to be strong.
Your 77kg obviously, so a 155kg squat would be great.
We used the overload principle with Max recently. He did 250kg 1/4 squats, then 165kg bench squats, then he smashed his PB with a 155kg squat @ 68kg.
He squatted 150kg last night, he came up so fast the bar jumped off his back by a few cm. You will see the footage shortly in the new video, amazing.
He squats in no-no-no fashion, no wraps, no belt, no spotters, off squat stands, not inside a power rack.
Does anyone still think that box squatting is no good?