I've just about decided to add a full-sized M&P as my dedicated house gun. I too can get that Qualified Professional .45 with night sights and three magazines at $499 delivered.
But for $455 they have the same deal in .40 or 9mm. But I don't stock .40 ammo for anything else, whereas I have a good supply of .45s. I would be dropping 5 rounds in capacity if I choose the .45 over the .40 and 7 rounds if I chose it over the 9mm. But I already have a ton of 9mm pistols and want something different this time. I've also already got a Shield in 9mm, and it's so good it has made me want to get another M&P. All my other .45's are 1911's.
Can anyone think of any reasons to go with one over the other? I prefer the recoil impulse of a .45 normally over the .40. Ammo cost is probably not a big concern given that I won't be a really high volume shooter. I used to be, but am old now and don't get out weekly.
I'd especially like to hear your thoughts if you have owned both.