A3 is a lot like A2, except brighter, lower output, and less low end. It's pretty nice for neck pickups when you want to volume match a lower output bridge, or bring a bass-heavy neck pickup under control.
Roughcast A5 is stronger than A4 (but less mids, so perceived loudness can vary). I'd tend to look more at Unoriented A5 or A2 for volume balance against the A3.
Another hack for controlling boom is putting shorter screw polepieces under the low strings, particularly in neck pickups. Getting some 0.5" replacement screw polepieces [I like hex, though the most readily available black ones look a little odd up close, especially only under 3 strings on 1 pickup] can really tighten things, and adds a hair extra bite that I really like on low strings, though I tend to prefer fatter high strings so stick with standard 0.75" screw polepieces there.
[Also on the hex thing, there's plenty of arguments that the only tone-affecting differences between hex & standard slotted screw polepieces are the standard length, and alloy. But hex heads tend to be made of a bit harder alloy, so it's a lazy way to filter out other alloys with a typically warmer effect on pickup tone. As long as you don't get a nonmagnetic alloy! Still, if looks matter to you, the most important thing is the reduction in length resulting in lower mass & inductance.]
