Ed hit the nail on the head....... the fps will rise when the power curve reaches it's highest point. Once at the top of the curve you will have your most powerful shots,,, as the curve goes down from that point on the fps will drop as well. The sweet spot on my .177 disco is right around 1700 psi, at that point my fps is a tad over 1000 and I get about 10-15 shots at that level,,, after that the fps starts to slowly drop as the curve goes down....
Jeff