Another idea. Think outside the .45 ammo box. You did not mention what the second gun is for besides sharing a pile of ammo, so what about this, if your second gun is to be a BUG or light travel day concealed: A 9mm or even a .380. Ammo is cheap enough that you might not want to bother with reloading, and the guns are going to be, usually, even more compact and light.
I've had the XD9 subcompact, and with Pearce grips it was very controllable and accurate. I still have a Glock 19, which is a bit larger but about the same weight. Outside SA, you have the Ruger LC9 and LCR or even the S&W Bodyguard in .380.
If you have not shot .45 in a compact, you might want to go rent one at a range. You might not like that big round in a little gun after shooting it. FWIW, I carry the XDm-45 concealed in all conditions (including 100+ degrees with matching humidity here in Houston), so my reason for having a smaller gun is just for the fun of it...and in case my wife, whose gun it really is, decides to start shooting again and get her CHL back. If I were cash flush enough to just have extra guns, I'd want something that was very different and just fun to go shoot.
Just one more thought.