I am also a Huge fan of short barrel BIG Bores!I like the 20-21" and had several 500,585 and 600s in that length with No regrets.My latest was a 500 Jeffery with a 16" barrel and am now duplicating it as we "speak" with a 600 OK also with a 16" Short and Fat Tube! Should be fun on both ends!....The 21" will balance well with your Gibbs and I promise you,all the guides in Alaska and PH's in Africa will want to buy it from you when they see and handle it!