Here I will look at a few stacks of armor units, making the same stacking penalty assumptions I did for the infantry and militia stacks from before. I focused on combinations of armor-TD-SP art. I can easily check out other combos, but I thought these looked promising.
First I went through even numbers of each brigade type from 5 to 10, and then I looked at doubling either the TD or SP art component. Note that going up to 10 armored brigades would require the tech to reduce armored's width.
Next I did some pairwise comparisons of the different armored stacks, and also to the infantry-artillery stacks from before. The armored stacks are much more powerful per brigade, but also more expensive. Also, piling on the brigades isn't very cost effective; it costs twice as much to put 10 brigades of each type in the same province for only 41% more firepower.
I was really surprised that dumping 12 Inf + 4 Art cost 1/4 the IC of the armored stack, but was pretty competitive in the attack stats. Of course the lack of hardness makes this combination much more vulnerable even with roughly equivalent defensive stats, and the manpower difference is huge.
The real value of armored divisions lines in the not-easy-to-quantify effect of speed on their operational utilization. Cutting off supply lines, encircling units, quickly reaching VP provinces to force a surrender, the above analysis doesn't really account for this.