It's all random variables. Paint age, company, quality, grade all help divide what is going to be what. Here in colorado, and I've Pm'ed sno about it, I've had paint recently that's .693, and about a month ago I had .696. Insanely huge paint, almost .70 Caliber. In CA though, you normally run from 685 to 689, so that's a solid bet to get something in .685. Maybe if you wanted to er on the side of caution I'd get a. 687. The only thing that might determine accuracy other than paint quality or underboring (which is running a tighter bore on the barrel to achieve a better fit) would be how the barrel is coated. Some companies have different coatings on the internals of the barrel that make them less prone to breakage, or easier to "Shoot through" and clean paint out of the barrel.
For example, as barrels go, I love SP All Americans. Great barrels, but if you get a break in them, the paint likes to stick to the inside and it's just hell trying to get a clean lane or even shot when you're in game, You've got to break it down fast and hope it'll work. On the opposite side of that, there's the Macdev Matchstik's which are sickening in how quickly they clean up, and how fast they clear paint while in a gun fight. That's personal experience. Now, that being said, lets go back to the thing about length - Anything over 16'' is too long, unless you happen to be running first strike rounds, and really know what you're doing, even then. We're not going to get into FS rounds, you can google that yourself. Why is anything over 16'' too long? Even on a woodsball field, it'll hinder movement as it's just this long protrusion that is harder to maneuver with, and it makes it a challenge to crawl through tight spaces or even be mobile with. The longest you'll almost EVER see on a speedball field is 16 inches, and that's because most speedball fields are air fields, with balloon-like bunkers. One of the things you use your barrel and marker for on those fields is pressing into those bunkers to get a better angle on your shot. A longer barrel there helps give you more leverage and more acute or obtuse angles to work with. Then again, this too is all still subjective to who you are, what your playing style is, and what you'll be doing on the field mostly.
In review -
12, 14,16 inch barrels, any size inbetween those is fine too (13,15,)
Bore size - .685 to .689 (Remember,.689 is on the big side.)
IDFK if you're still using that autococker, if you are remember it's a CLOSED BOLT MARKER, and you WILL need to add in a small piece of tape or a dab of clear nail polish on the inside of the barrel to help hold the ball in (It's just due to how the marker works. If you don't know how it works, then you might have missed reading this thread which I'm pretty sure I posted to you, just so you had some good info to read, but hey, refresher course! http://www.pbnation.com/showthread.php?t=3655911
middle of the page, Big orange and green diagram of an autococker with a slider triggerframe)
Hope that helps.