Re: A3 PAF
It's the weakest of the commonly used guitar magnets. Its main effect is to lower the output of the pickup. You get all the effects of a lower output pickup: Less saturation of the amp, resulting in more clarity. Less responsive to the strings.
If coming from A5, it's a big drop in output. Coming from A2, it's minor. I think of A3 as "Diet A2" and A4 as "Diet A5." If you have an A2 powered set, and one of the pickups is a little too hot to match the other, put A3 in that pickup. If you have an A5 powered set with a similar issue, put A4 in the one that's a little too strong.
I have attempted to use it to tame firebreathing pickups like the Gibson 500T. No dice. It cuts output, which helps a little. But there's no way it can get rid of the congested and treble-weak e.q. of heavily wound coils.
My takeaway from this and other such swaps? Magnets mainly affect output, not e.q. The different e.q. largely comes from how the change in output interacts with your amp and your technique. People love to talk about the "e.q. of magnets," but based on what I've tried, I don't exactly buy it. I mainly hear differences in output with mag swaps, not fundamental changes in the e.q. of the pickups.