If you are considering dropping that kind of dough on a second set of barrels, and it is an option to do so, you should consider two different gauges (20 and 16). This would give you much more versatility than two sets in 20, and I'd be willing to bet you would end up using that small-frame 16 more than the 20 (really a much better gauge for hunting, but that's a different debate).
Otherwise, go with one set choked IC/Mod ... choke is vastly overrated as a factor in hunting success. Save the $2400 and buy second gun -- a used double with tighter chokes and a lifetime's supply of top-quality upland hunting ammo. My two cents. Happy hunting. TT
