Fladude
You are getting some great advise. Now let me through in my 2 cents worth.
I would definitely make the SCI show or I would go to the Dallas Safari Club show in about 2 weeks Or both. You will get the chance to see and handle many double rifles and talk to some experienced people.
I would try to find someone who will let you shoot a 470 and a 500 so you will have that first hand experience. I personally think the 470 would be a better choice because of resale, availability of loaded factory ammo cheaper cases and a wider selection in bullets if you reload. While recoil is a subjective thing I feel the 500 has a significant step up in recoil over the 470. Think 470= light 12 with slugs 500 = light 12 both barrels with slugs same time. Perhaps I am exaggerating but not much.
The good thing about buying a “NEW” rifle is you can have the stock fitted to you. This helps with the recoil.
Hope this helps
Bill