XD9--3,4 or 5"?

I have a 5" 45acp XD and it is my favorite semiauto I've ever owned. Freed up some cash and am thinking I'd like to buy a little brother to the 45. I already have carry guns (3at and SW 642), but it might be nice to be able to carry the 9 if I felt the urge. But I don't want to sacrifice much/anything for concealability, because I feel the 9mm is not the best protection round (please don't try to sell me on switching over to 9mm primary carry--that decision is over for me). Just think it might be nice to be able to do both. Mainly, I want a decent home defense gun (got plenty of those as well) that'll be fun at the range, but in a cheaper cartridge.

Which length, and why.

Anything wrong with the 3"?

Why the 4 vs the 5"? or whatever else. Thanks for all your help.

Well, 9mm works pretty well in a 3" barrel. So compact 9mms make a lot more sense than the compact .45s IMHO. While a 5" or 4" 9mm will certainly sizzle, a 3" will not be degraded much. I believe the same goes for .40.

I have a compact 9mm and it is great. A near pocket pistol sized platform that performs like a full sized service sidearm...gotta like that. If you have some full size pistols, get a compact...I sure like mine. (M&P 9c for me)

You can get the sub compact XD and get the extended grip/magazine for it.

I've also got the XD45 5" and I'm planning on getting the XDm 9mm to match, and will go for the 5" model.

I've got enough compacts and I'm in a full-size-faze right now. Most of my future purchases are going to be full size, hi-cap, all out models.