I just talked to Fred at Bullberry fairly extensively about barrel length for my new barrel in 6.5x284. Fred strongly recommended going with a shorter barrel for accuracy. I know that there are a number of guys using long barrels for 1000 yd. competition. The main reason for the additional barrel length is to gain a few feet of velocity which is only really useful at extremely long distances. Fred's contention was that the loss in accuracy due to the extreme barrel length and the poor balance that such a long barrel causes in an encore really just isn't worth it.
Most of the guys shooting 1000 yd. are using bolt guns with 1.25" Full Bull barrels that weigh a ton. In an encore the barrel would be slightly smaller in diameter but still pretty heavy. Because of the short action it just doesn't balance well with that long, heavy barrel. I guess given the great comments I've gotten from everyone that has one of Fred's barrels, and what I really intended for the gun, I decided it was smart to defer to the expert so to speak.
I'm sure he'll build you anything you want, but I'd definitely recommend a chat with Fred on the subject. He changed my mind regarding how valuable it really is. I was originally going to order a 27" barrel and he convinced me to the point that I finally ordered a 22" barrel.