Normally, the accuracy difference in barrel length comes from the increasing sight radius as you increase the barrel length. I suppose you could get a tad more velocity from longer barrels which could give you a tad more consistency, but I doubt it has much affect. That being said, I believe I see a bit less sensitivity from ~7" barrels than I do with 5.5" barrels. That too may be a figment of my imagination.
I believe barrel length is more a matter of preference.