the 5" has a proximity fuse. If it gets near a plane the round will explode. Its possible to hit and kill with that beyond icon range. I dont have any solid documentation on the other two guns but from experience the quad can kill a plane out as far as 3.5k, and the 20mms out to 2.5K. In both cases it is hard to lead the shot and hit a plane from that far out. But in a field or ship gun, you have a large amount of ammo to work with, so there is no harm in trying. Most important part is learning how much lead to use with any of the guns.
You can practice this offline if you like. I do not remember if the lead computing site is enabled by defult for offline use, so just in case, this is how you turn it on:
Clipboard>options>arena setup>enviroment>arena settings>
Double click on flight mode flags, and there will be a checkbox for enable lead computing site.
To use it, you look at the enemy target, and press the tab key. A box will appear around the target icon, and a green + will show the aiming point you need to use.