I did a side by side comparison of the Winchester Low Recoil 00Buck 2 3/4" 9 pellet Ranger stuff,......right next to good ol' Federal 2 3/4" 00Buck we all know and love....
One shot, followed by one shot. There is a very noticeable difference between the two. The target however, showed the same damage. Sorta splitting hairs....
If it were me, I would stick with the 12 and get the low recoil stuff. However,
Do you have young kids that are going to shoot it?
Is this going to be just for clays? Or is hunting/SD a possibility?
You already have a nice bunch of scatterguns, and Bass Pro, Cabela's, Gander Mtn., etc,... sell these nifty shooting shirts with padding, on the shoulder in the latest Fall colors....

The 20g is a fine balance between effectiveness, purpose, and somewhat reduced kick. But, I'd stick with the 12 in a semi version, but YMMV....
Keep us posted and Good Shooting.