Usually - go with what the fuse panel says.
The manuals are written by people - and people make mistakes!
I've found several errors in the factory manuals, and the owners book is no
different.

Besides that....
You're not supplying more or less power to the circuit.  You're just letting
more or less current flow before the fuse blows.
5 amps is nothing anyhow.
If it was a toss up between "do I stick the 5 amp or the 25 amp one in" -
well yeah, it's time for research.  20 or 25 you'd never notice!

Hi -

 I have a 1987 Fiero GT and while changing a fuse (for the coolant fan
relay coil) - I noticed something very odd.

 In my owners manual (Yep - I'm the original owner) - in Section 6.8
it has a diagram showing the layout  and to the side designates which
fuses (by color and amp) go where.
Incidentally, besides in the manual - if you wipe away the grime by the
fuses - it also tells you the proper amp to go in each category.

 Well - lo and behold - as I removed some of the grime where the fuses
are - I noticed the last fuse (#17) very clearly said 25 Amp CTSV-Lid.
(which is for the rear compartment lid release and light, power door
locks relay and power sport mirrors control) - YET the Manual says
it should be a 20 Amp (which was the one being used)

 My question is - which do you think is correct - and can using the
incorrect one cause problems. If the manual is correct (20 Amps which
is what was being used) - then no problem.
However, if the Fuse Box data is correct (and the manual incorrect) and
it should be 25 Amps - that would mean I am and have been supplying 25%
less amps. If I put in a 25 Amp fuse assuming the Fuse Box is correct
and the manual is incorrect - if that turns out to be wrong - then I
would be supplying  25% too much.

 Which is worse - too much - too little - or 25% difference wouldn't
matter?

Thanks for any insight anyone has on this..
  Rick