Get a 20ga Beretta BL3 or BL4. It'll weigh a few ounces less than 6lbs, it's got a steel frame, nice and svelte, and they aren't all that expensive--you should be able to find one around 1000 without trying too hard. A lot of gun for the money if you ask me. 26" barrels with a cut stock would be just the ticket. 7/8oz field loads are no issue with recoil in the field, load up some 3/4oz shells for the range and you'll be all set.