I've always been a .45 kind of guy. Something about 230 grains of lead hitting animate objects that really puts them down in a hurry. 9mm on the other hand have been known to take more than one shot to get the job done. That's why a majority of police departments switched to .40 calibers.

The .45 seems (to me anyway) easier to shoot well since the recoil is not as "snappy" as with the 9. I've always experienced more muzzle flip with the 9 than I have with the .45.

If you don't need the 870, and you like the handguns, I'd make the trade and wouldn't have any reservations.