bjlooper'
You have not told us how much big bore rifle experience you have. Also you have not stated if you are looking for an English double or a new made double.
At the DRSS hunt I shot jjs's 470 and clarks 500, both Merkels, as did several other DRSS members.
The general consenus is that the 500 kicked a LOT more.
I did not find it painful in any way, it just shoved you farther back, and the rifle rose higher. It did not "bang" my hand or my trigger finger.
However if you do not have a lot of BIG bore rifle experience, and you are getting a new made double, I would go with the 470. In a British double any calibre from 450/400 to 475 No2 would be excellent.
Before you buy you should go and shoot a double rifle or two.
If the new made double you like comes in 500/416, that too would be a great choice.
If you do a search you can find some pictures from our last DRSS hunt. All of our doubles are pictured.