Speedflex lines thread. Brake system

Hi, I am from Venezuela, FSAE-LUZ. Actually, we are reactivating our team since 2010. We have some doubts about the last prototype. One of them is the brake system distribution.
The old team used a ¾ “ bore for rear brakes (Wilwood master cylinders) and 5/8” bore for front brakes. The thing is they were using speedflex lines threaded -3 AN for front brakes and -3 AN for rear brakes until the residual pressure valve . After the valve, they changed for speedflex lines threaded -4 AN.
The rear calipers are smaller than the front calipers ( Wilwood PS-1 vs Wilwood Dynalite single) . What is the difference between the speedflex lines -3 AN and – 4 AN for brake system applications? The only thing I know is both of them can be applied for 2000 PSI and have different internal diameter. Should we change all our brake system to -3 AN thread?

The Distribution for rear brakes is:
¾” bore master cylinder / -3 AN speedflex / hard line / Residual pressure valve (2PSI) / -4 AN speedflex to tee (-4 AN male-male-male).

-3 is most common for brakes. If part of your lines are -4, I don't see any reason to change.

Further to what Jonny said,

You may be able to lose some brake system mass (smaller lines as well as less fluid) by running -3 as opposed to -4. Given the very low fluid displacement you should be getting and the pressure rating of both line sizes, either one should work just fine.