I get this question all the time from my customers. They say they want all the accuracy possible but in a packable rifle. Then they say they want +1000 yard reach in a sub 8 lb rifle........ Considering thats about the same weight as a Remington BDL, thats asking quite a bit.
Smaller contour barrels can be extremely accurate and consistant. The heavier the bullet your using, the longer the bullet, the higher the velocity its driven to, the more stress the barrel has to endure consistantly to get the bullets to hit point of aim.
In my opinion, chambering size and velocity range has to go into consideration. If your building a 270 to shoot 130 gr bullets at 3000 fps, that would require a certain barrel but if your talking abour driving a 338 cal 300 gr bullet to the same 3000 fps, I would not recommend the same barrel for both.
For your needs, I would recommend a minimum of a fluted #6 contour. Not because anything lighter will not be accurate but because you want to shoot out to 1000 yards and beyond. As such, we need enough rifle weight to dampen your ill effects on the rifle to ruin accuracy.
Don't take that the wrong way, all of us as the pilots are the weak link in a long range shooting system. In most cases the rifles will do the job as long as we as the pilot does not get in the way of success.
I like to see a minimum of 10 lbs of rifle weight for any rifle to be used out to 1000 yards. The more the better but this is my recommendation. This amount of weight will help dampen heart rate and breathing, not to mention allow enough weight to settle well on the bipod and rear bag.
If I were to build myself a rifle for your needs, I would go with a fluted #7 contour and put up with the weight of a 12 lb class rifle ready to hunt with. When its time to pull the trigger you will be happy to have a bit more weight.
You can certainly make light rifles that shoot extremely well. I have a 7.5 lb 7mm Allen Magnum that just does not seem to miss(knock on wood!!) and I have used it on 28 head of big game from 400 yards to 923 yards with only ONE miss. This rifle has a #3 contour barrel but I will freely admit I prefer a heavier rifle for big game hunting at ranges past 800 yards.
Hope this helps some.