The lower the FPS the faster the pellet drops. The more hold over, the harder the shots. Yes, you can holdover but why not have a flat tragectory to start? Why make it harder than it needs to be? FWIW, this isn't competition, 925fps is accurate enough. If it's a head shot, how much FPE is needed for a pass through at your distance? Why use more fpe than needed? Why not have flat? Don't get caught up in larger bore is better. It gives you more fpe but these are iguana's not coyotes.
All JSB using Hardairmagazines's BC
.177 8.4g 925 fps at 25 yards 11.54 fpe, 1.42" drop at 25 yards
.177 13.4g 925fps at 25 yards 23.1 fpe, 1.31" drop at 25 yards
.22 18g 880 fps at 25 yards 25.9 fpe, 1.49" drop at 25 yards
.25 25g 600 fps at 25 yards 16.96 fpe 3.19" drop at 25 yards
American Airguns - Trajectory Calculator
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Ballistic Coefficients
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He already bought a .25 air rifle and scope clicks negate drop concerns. OP also mentioned a coyote problem which typically would lend itself to a larger caliber, as you have pointed out.
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