What are you actually wanting to know? I only shoot pellets, usually 10.3+ grain pellets in .177.
I shoot .177 exclusively for pesting in my backyard for the most part. Anywhere from ~750-850fps. I don't go higher than that because the noise level gets too high for my situation and I have found that shooting out to near 100 yards, when I hit about 880fps, spiraling becomes an issue.
So, what do you really want to know? There is no single best fps for all airguns. No matter the caliber. Each gun/barrel is different although there are some reasonable assumptions that can be made if given enough information.
However, you asked a broad question for which there is no definitive answer... if I am correct in discerning why you asked it in the first place?
All my best!
Kerry