IMHO shooting ANY slug gun off a bench as if it were a rifle is just begging for a flinch to set in. Hunching over the gun at the bench is going to magnify recoil, and even if the gun fits you, if the bench isn't a good fit it'll be pretty brutal. I know you need to isolate the gun from the shooter's wabbles and weebles as much as possible when zeroing, but there are better ways to do it. Look into a Lead Sled (
http://www.amazon.com/gp/product/B00...J7DYZFJNTKR8YQ ) for example. If you are satisfied with the gun you have in other respects, once you get it zeroed to your satisfaction I doubt you'll be shooting it enough in the field for recoil to be a problem. And if you're like most of us, you won't know there was recoil when you squeeze the trigger with a buck in the crosshairs anyway.
And I bet the little 20 will carry better afield than most anything else...
fwiw,
lpl