Before you scoff at the idea of a shorter barreled 338, here is some good info. I have a 22" on a Tac338 action with Shilen 8 twist barrel, (9 would be fine, just happened to have an 8 available when I bought it)
-2720 fps (92 gr H1000, 300gr SMK) no pressure
-1000 lbs of energy past 1800 yds
-supersonic past 2000 yds
-7.4mils to 1k
Those numbers are real life and very good any way you look at it. If you want a 30" benchrest rifle, good luck. This isn't a BR site so I figure you want something practical as well as accurate. adding 6 inches to my barrel might get you an extra 150 fps, but at what cost? extra storage space and weight and maneuverability. Not worth it to me. I have had too many long barreled beasts to go back that way. Esp if you have to carry it anywhere.
Another interesting fact is Barrett offers their 98B with a short barrel for a reason. Their research team sees the positives of a more compact, highly effective weapon.
Good luck,
DT