With respect, I think Jerry is wrong. Light bullets (.223/90) don't get blown around more than heavier bullets (.308/155 or 185).... _all_ of "how much is a bullet blown around by wind" is incorporated into the "bc" parameter plus the muzzle velocity. Exactly that, and nothing more. If you use an accurate BC (and nowadays, thanks to Bryan Litz, we have *good* G7 BCs for the bullets that interest us, and they are all done on an apples-to-apples basis), then your ballistics program tells you the truth - this goes for vertical wind as well as sideways wind.
For shooting iron sights ("TR"), the rules say that we can use any weight bullet in .223, and any bullet <156 grains in .308.
For scoped shooting ("FTR"), the rules say that we can use any bullet weight in .223 and any bullet weight in .308.
If you do decide to build a .308, any barrel twist in the 1-11" to 1-13" range will do you fine. Get the best barrel you can find (Krieger, MacLennan, etc).
For iron sights, 30" barrels are usually chosen. Part of this is to get every last bit of speed, another part is simply to get the front sight a bit further out (it's easier to keep the front sight element and the target image in simultaneous focus that way).
For scopes, you can have a somewhat shorter barrel. 26" or shorter would be unusual for a 1000yd rifle, we tend to be speed hogs; the vast majority of FTR rifles have barrels in the 26"-30" range.
In scoped (FTR) shooting, the Berger 185LRBT is the "go-to standard". The recently-introduced Berger 185 Hybrid is probably fractionally better. There is also some cutting-edge work being done on shooting heavier bullets (210-230+), however that is not yet well established as a match-winning setup.
Having said that, a .308 shooting one of the modern high performance 155s (Berger 155 Hybrid, Berger 155.5 Fullbore, Sierra #2156 Palma) is *very* close in performance to a Berger 185 load. The top 155s are lower performance, but only barely (in the sense that you still might be able to win a national or international championship match with the 155s; but all other things being equal, the 185s do have a single-digit-percentage edge over the 155s).