Speaker magnets

There is always a trade off.  The magnet needs to match the designers goals.  Large magnets do increase efficiency.  They also roll off and limit low frequency extension (all other variables being equal).

Most modern speakers do not have anywhere near the size magnet or magnet strength of a good vintage speaker at all, nor anywhere near the voice coil size and type and amount of wire around the coil, which gives the vintage type driver a tremendous advantage in efficiency and control over cone motion. They use a type of magnet that does not deteriorate over time as well as a fiber surround that does not deteriorate either. I have 70+ year old vintage models that work and sound like they were made yesterday because of these reasons.

Plus 1 on weirdness and magnets. Can be very creep and/or surreal. Normal stuff like a fire truck using its flashing lights (no sound) and coming up the mountain road right by you, seems like a religious experience. But at least you realize why it’s happening (well placed warning signs that recommend limited exposure times). 

Bigger is not always better in woofer magnets. You need the right amount of gauss(related to magnet size) to give the right driver specs for the bass enclosure design to produce the bass control and roll off desired. Too small a magnet and you get boomy bass. But too big a magnet and you get over damped bass which starts to roll off too high and you end up with less bass.

The OP will need the Thiel-Small parameters for his drivers to design cabinets for them. These equations supersede the old cut-and-try method.