I've had both the Beretta and a Neumann/Silvers over the years. Have since parted with both. Bought both of them at different times from the Hamburg Cabelas. Bought the Beretta for under $1K and the Neumann for $1200, which are great values. Unfortunately, the blue book tells people to sell the Neumanns for $3K, but I've never seen one sell for that. Cabelas had two at the price for a long time, then marked them down under $1500 to move them. Both are good quality, but the Neumann definately seemed to be the better built of the two. It's a first rate boxlock and nicely balanced. 10 gauge bismuth has been discontinued, but you can still find it occasionally on the auction websites and Albrights gunshop in Easton MD used to have a good supply. RST now makes some as well. Chambermates will allow you to shoot 12 gauge ammo, and some of the SXS shoots permit using them as well.
Here are some photos of a recently sold Neumann:
http://www.cabelas.com/european-shotguns-neumann-boxlock-10-ga.shtml