I have >600 watts of lighting and my return pump on one 20 amp GFCI breaker, and it has never tripped in the 2 years it's been installed. We first set it up with a GFCI receptacle and it would trip as soon as the halide ballasts tried to fire. My powerheads, doser, ATO, and skimmer are all on another 20 amp breaker with GFCI receptacles.
In my fish room I have 3 quad receptacles each with a GFCI receptacle that are all surface mounted by an electrician. There are also two standard in-wall dual receptacles in the room that were both plugged with those kid proof covers. I was short one plugin and decided to plug a Mag 3 pump into one of the in-wall receptacles to mix saltwater. It ran that way for several months without a hitch, and I forgot about it. I was away for the winter working in Alberta and I receive a panicked text message from the inlaws saying there is a firetruck at the house (ya thanks for the details!). It turns out the Mag 3 decided to seize and proceeded to overheat and the receptacle caught fire. Luckily there wasn't anything near the receptacle that would catch fire or the whole house could have burned down. Apparently the whole house was full of smoke, and I had to paint over the 18" black flame marks up the wall. When the receptacle caught fire it did eventually trip the (normal) breaker in the panel. If it was GFCI the receptacle probably wouldn't have caught fire to begin with.
Moral of the story, Murphy's Law says it will be the ONE unprotected receptacle that will happen to have the ONE piece of equipment that will fail and cause your whole house to burn down. Now, all my fish related receptacles are protected. They have saved the bacon numerous times.
I had a similar thing happen with a different mixing pump on a GFCI receptacle and it tripped the breaker at the very first spark. I was actually standing within 3' when that happened. Nearly pooped my pants.
I also had a newly installed algae turf scrubber fall over in the sump overnight. It then shot water 4' up the wall directly at the plugs...
of course. This tripped the GFCI and saved all the pumps in the sump that would have run dry otherwise, it also limited the amount of water on the floor. I slept like a baby through all this and groggy in bare feet before my morning coffee I walk in the room and wonder why the heck my feet feel wet. An aquarist wakes up
real fast when the feet get wet for an unknown reason.
Moral of those two stories, GFCIs are multi-purpose tools.
You have to figure out what you're comfortable with for yourself, and then you have to try to sleep at night for the first week it's running.