Warning: the art of sushi mathematics is treacherous. Proceed at your own risk.
Assuming a standard sushi roll with 6 pieces and a radius of 5 cm, we can calculate the derivative of sushi-fulness as follows:
f(x) = 3.14x^2 - 2.5ln(x) + 5.6x^4
Where x is the number of pieces per roll and f(x) is the deliciousness factor.
Read about optimizing with Gaussian Processes