Db, I think the writing is on the wall already, your next lens will be 600II.
From the standpoint of shooting dynamics, here is a complementary type where the focusing distance doesn\'t change much/quickly like in head-on shots, but the problem is in the AF acquisition while doing a fast swing with a long heavy and thus very \"inertial\" lens. This type of shot becomes much easier quickly as the distance to bird increases and the required angular speed of the lens drops.
