My Veteran long shoots the 18 gr JSB at 940. I found that the 15.89 gr JSB usually shot good at 910-920 in an FX400 and a Streamline and a Diana Outlaw.
A lot of guys find that 880 to 900 fps for both 18 and 15 gr is the magic spot. I like em a little faster.
I've also had good luck with the Crosman ultramag 14.3 at varying velocities from 700 to 925 but it all really depends on what the gun likes.
My .22 Huben shoots 25 gr JSB at 1040 or so.
So as you can see every gun is different. Just have to find out what it likes.