A Stevens 311 was my first SxS, followed by a Model B and both were 12 Ga. shotguns with 30" barrels. They are heavy and in my case slow to respond to a fast moving target. Thirty years ago I bought my wife the 311's predecessor, a 1940 vintage 16 Ga. Model 511 Stevens. The 16's wood is much better than the previously mentioned 311's and the gun's 26" barrels make it more responsive than my experiences with 30" barrels. I'm not sure about new 311's, but the older 311's are built to last and it might be a good idea to buy a used gun. Your choice of 20 Ga. is in my opinion a good one for a first SxS.

Jim