Imtiaz Gandikota
Ansys Employee

If you ran all 4 iterations, please look at history of 5.1 design. This design is the ls-dyna (computed) result of optimum predicted by the metamodel in iteration 4. If metamodel is accurate, design 5.1 will be the best optimized curve. 

Note that, if the metamodel is not accurate, it is possible design 5.1 may be worse than other computed designs and you may have to run more iterations. Optimization history plot should show the accuracy/difference in MSE between computed optimum and predicted optimum.

History plot under "Metamodels" in the viewer can be used to plot predicted histories.