For timed cuts, a plank was clamped into a test rig and cut with a saw attached to a pivot arm. The nose of the tool was weighted to provide downward pressure - approximately 23 pounds at the blade.
The test plank consisted of a piece of OSB sandwiched between 2x6s and capped with drywall and more OSB. The central piece of OSB was flanked by 12 rows of nails - so the recip blade had to cut 12 nails each time it went through the plank.
The author used a stopwatch to time cuts through the test planks. A blade was considered dead when it took more than 37.5 seconds per cut; by that point, most blades could barely get through and were hot enough to char the wood.
Tooth size alone is not a good predictor of longevity. The widely spaced teeth of the Ridgid blade (at top) cut quickly at first but were prone to snagging on nails. The more tightly spaced teeth of the Starrett didn't lose teeth to shock, but friction and heat eventually wore them down.
The author tested for resistance to abrasion by sawing through shingles sandwiched between pieces of OSB.
As was typical of the bimetal blades tested, the teeth at the center of this model (shown after 22 cuts) were completely worn away. Only the carbide-tooth blades survived for long in shingles.
Both of these blades are Demo Demons; the lower one has made 126 cuts through nail-embedded wood. Although the carbide tips have been dulled, they remain intact and can still cut - though at a slower rate than when sharp.
Lenox's carbide-toothed blade may not cut nails, but it's great in abrasive material. The blade at the bottom was still going strong after making 122 cuts through shingles and OSB. The tips were worn but not damaged.