The 2019 24 in red and green, IPAL in blue and pink.
Sealed are both 6cuft.
Ported are both 12hz in their optimal sized boxes.
I noticed that the 24 has more xmax and xmech than allowable PE, the IPAL has enough PE to exceed it's rated xmax in just about any box size or type. I also noticed is that neither are exceeding their xmech... even with given something excessive like 7kW of burst-power going to either...
As I already said: if you have limited space, the IPAL does really well. Otherwise, multiple cheaper cones will likely give you better results.
Now let's look at it from a price-perspective:
Here is $2400 worth of IPAL's, RBX's and PA-460's, with no bulk discounts factored in.
All ported at 20hz in their optimal boxes.
460's in green, RBX's in Blue, IPAL's in Red.
The price is really starting to hurt the IPAL's, but ONLY if you have the space for all those boxes for the cheaper drivers...
UM-18's would be slightly more expensive than the RBX's, and lacking a fair bit of mid-bass, but making up for it when tuning below 30hz in small spaces...
It's worth noting that the 460's are only at 67% power here, and the IPAL's are at max power.... and the RBX's are at about 85% power.
The IPAL have no thermal headroom in this configuration, they are being "stressed to the max" trying to produce this much bass. That's lack of total-cone-area for ya...
At the end of the day, it really depends on your budget, target frequency, and available space.
For horns... that's where things get tricky. I don't have that much free-time to model that!