A lighter wallet. You will get no noticable recoil reduction and may cause yourself issues with the gas system and ejection problems. The pattern thing is subjective at best. Leave it alone and shoot several different patterns with different ammo and different chokes. You will also reduce the value of the gun to most buyers.
May already have been... The Optima barrels, as compared to the earlier Mobil ones, have a much larger bore and longer forcing cones standard from the factory. Optima barrels only available on 12 gauge.