I would do 5A normal..

It's ok to under fuse, but never over fuse

Either would should work fine and wont damage anything.

Thus, both of his choices would be fine.

EDIT: agreed - either should be fine.

A 4A SB will be fine,it will last without a problem with leds installed until you get a 5A

You could try an auto parts store.

I picked up 5Amp fuses at Home Depot in NJ.

Auto Parts stores or hardware stores like Home Depot or Lowe's might have them depending on the location. The big issue with both is finding slow blows as the majority will be fast acting in stock likely at these places.

Pop the 4aSB in there and forget about it. It won't draw more than 4A. If it does with LEDs in there, you've got other issues.

Rule of thumb is never use a SB somewhere that needs to be shut down immediately if there is an issue, like a logic supply (+5v).

The reason 5ASB are in the G.I. to begin with is to prevent the sudden inrush of current from the transformer on power-on from popping a FB fuse to incandescent bulbs. A FB breaks down over time from these spikes in power-on cycles. I think it was meant as a durability measure, no immediate harm in slowly powering off the G.I. section, as it runs on AC anyway, those fuses are solely there to protect the transformer, no rectification. The rectified sections need to pop off right away though, or they'll burn up the bridges and/or other parts.

Someone correct me if I'm wrong here.

I agree with you 100%.
The FB fuse will blow sooner than later in that circuit if you leave it in.
4A SB will last just as a 5A with leds,may as well leave it in.

That is an interesting thought. That might mean that you could damage things because the load is less due to using LEDs. The original fuses might be oversized.

How would you damage it? Basically you now have a circuit designed to handle 5 amps and it is no longer pulling that amount.

If you have a short or something faults or fails, it would be cleared out quicker with more load and maybe won't without the incandescent lighting load. Ideally, your fuse should be set not at what your equipment can handle but slightly above your maximum load current. Switching to LEDs means there is more margin between your load and blowing the fuse.

I thought about this too. My thoughts are if there is a short on the GI line, it'll pop a fuse just like it always does, regardless of LEDs or AC bulbs. The transformer secondary tap and power is what determines the amperage for your fuse selection, that is the draw limit you are protecting and do not want to exceed. You're solely protecting the transformer from burning up. So it will pop a fuse regardless of whether LEDs are the load or incandescent bulb with a short. Just because it is drawing less current for LEDs doesn't change the design of the transformer. The only difference is that with LEDs, they're all internally rectified, so they're a little harder to short out.

But yes, technically if you are using all LEDs, you could roughly calculate the draw and lower the fuse value accordingly. No need for 5a fuses when using LEDs. I'd imagine you could get away with 2 amp fuses in most cases. Depends on the voltage drop of the rectifiers used and resistor value, but I can't imagine single LED bulbs are drawing more than like 10mA each. At that rate, 200 bulbs would draw 2 amps. I dunno any games that have 200 bulbs in them that are always on.