This post is a little old, but I will add my two cents anyway....
First off, let me say that I am a serious dyed in the wool .45 guy, BUT I have seen the first hand results of a .40 when used against a determined bad guy. The .40 worked well. That is not to say the .45 would NOT have worked as well or better, it just wasn't in use at the time.
One of my favorite comments when this argument is brought up, is, "a 9mm/.40 cal MIGHT expand with good ammo, but a .45 will NEVER shrink."
The .45 does have a much softer recoil impulse, and on average the single stack guns are easier to fit in the hands of most shooters, when compared to the double stack guns of the .40/9mm size. I am with 40 Rod on this one, capacity should not dictate caliber. Having the weapon fit the shooter is more important than capacity. You can have all the ammo in the world, but if you do not shoot the gun well, you might just need it. A few well placed shots will solve more problems that alot of poorly fired rounds... My department currenly issues the 8+1 shot Sig .45. I have been teaching officers to re-load this gun and manage thier ammo for a long time now, and it has never once been an issue on the street. When I am teaching at our state academy, and the single stack shooters are surrounded by those with large capacity mags, all I do is make sure they have MORE magazines and that they stay on top of thier reloads. They are not handicapped in the slightest compared to the 15 round .40 caliber guns on line around them.
I have two personal guns that make a great comparison for the recoil difference between the two rounds. I have a service model Springfield XD in .40 and one in .45. The .40 cal has a 10 round mag and the .45 has a 13 round mag, due to the former restriction on magazine size when I bought the .40 cal. There is no perceivable grip size difference between these two pistols. They fit the same holsters. When you shoot them side by side, the .40 caliber gun will "snap" in recoil and the muzzle will rise higher. The .45 will "push" in recoil and maintain a lower muzzle rise. Most shooters find that they can control the .45 better in recoil, and shoot the gun FASTER as a result. Both guns are about equally as accurate.
My department carried the .40 caliber for 7-8 years before transitioning away from it and to the .45 about 5 years ago. We left the .40 cal because it was beating our guns to peices and we were fighting with manufacture to fix the problem. Since having transitioned away from that gun/caliber we have not had any pressure related maintenance problems, and as a whole the departments qualification scores when up on average 32%.
One other consideration, bullet penetration... Heavier bullets penterate deeper when impacting barriers than lighter bullets. If you work in the cold where people dress heavy in the winter, or if you are in a position to shoot through a lot of auto glass, the .45 will work more efficiently than the .40.
Ok, enough.. I am off my soapbox... thanks for letting me blather on...