The 40 will push a wider 180 as fast or faster, in many cases, than the 9 will push a 147. I believe this matters for little problems like the FBI shooting referenced earlier in this tread; and I am certain it matters on large attack dogs, etc. I was skeptical of the .40 S&W when it was introduced; but I've seen it work in the field for a couple of decades now and I'm convinced it's a better mousetrap.
If you choose the 40 over the 9mm, there are trade-offs such as increased recoil and costlier ammunition; but many .40 S&W autos can easily be converted to 9mm- but the reverse is not the case. And yes you will give up a few rounds of capacity with the .40, in like-size guns. For the ability to use bigger, heavier bullets it is a trade many of us are happy to make.
“Nine-tenths of tactics are certain, and taught in books: but the irrational tenth is like the kingfisher flashing across the pool, and that is the test of generals. It can only be ensured by instinct, sharpened by thought practicing the stroke so often that at the crisis it is as natural as a reflex.” ~ T. E. Lawrence