I've made the claim several times that the .40 and 10mm aren't that different. Factory load of Longshot in a .40 in a Glock 35 (5.3") will hover around 1250 fps with a 180gr, if you work up slowly it's not hard to get around 1300 fps (a 6" will only give more fps). I've loaded a LOT of .40 and 10mm and yes the 10mm does have a little bit of a velocity edge simply because it can hold a little more powder, but that's its only advantage.
However the .40 case is stronger and overall more efficient (ex. 6.5gr of Unique will give 1240 fps from a 6" .40 S&W with 180gr, below book max and it comes out almost 95 ft-lbs per 1.0gr of powder. That's a stout but safe load that doesn't eat much powder. The 10mm could do that too, but it'll eat more powder to match the .40's velocity.) The general overall mistake most make when comparing the .40 and the 10mm is that they've come to accept that HOT 10mm is somehow no longer hot but rather normal whereas in their mind the .40 will never be anything more than a 180gr @ 1000 fps cartridge, both being incorrect.
Also most published load data gives the 10mm two advantages over the .40, one is a longer barrel (usually 5" for 10mm and 4" for .40) and they load the 10mm to higher pressure almost always, which isn't fair since it's not stronger than the .40. I've made the claim that if you were to load them both to the same pressure (as close as possible at least) and use the same barrel length (and bullet of course) that in many cases the 10mm would only show about a 75-100 fps advantage, if that.
I've never claimed the .40 is more powerful overall than the 10mm is, but it has its advantages over it for sure. I don't think there's anything living that would know the difference between a 10mm and a .40 S&W. The way the 10mm crowd thinks it's a wonder they're not selling their 10mm's to buy .40 Supers, after all it's more powerful than the 10mm. However I'm sure they might agree with me when I say that despite more "power" the .40 Super probably really isn't going to kill anything that the 10mm can't.
Likewise, what is the 10mm going to kill that the .40 S&W can't? If you keep the comparison at least somewhat fair, there is no real discernible difference in the ability of either one.