Hi samg, the best advice I can offer is to make it known at your local grounds that you intend to upgrade your Lincoln. From my own experience most regulars will be happy to let you try out their gun. Be warned however that, as in all things, the user will generally be biased towards their own make and model. Similarly the grounds will normally have a room full of o/u 12's you could try.

With reference to your the weight of the gun i would be more concerned about YOUR size. Our eldest lad is 17, 5'5" and builty like a racing snake. Wielding a 20b he is a good shot but is simply unable to comfortably hold and swing a 12. He works at our local clay ground and has been unable to find a comfortable fit. A 20b is just as capable of breaking clays!

All the best!