Joerg:
I shot National Match Course for more years, mostly with iuron sights, as well as a lot of 1000 yard. Started out with an old service grade M-1 and handloads. When I could see, I used to fire in the mid 90's on the old 5V target, with the M-1.
I "graduated" to bolt rifles, having shot the M-1 to death, more than 10,000 rounds, most of that in actual competition. Used Model 70 Standard Target rifles in 30-06, and a Remington 40X in .308. Personally, I always leaned toward the Model 70, which I fired off the left shoulder, rapid fire strings included.
I have seen people do well with Savage 110's also. Out to 600 yards, I believe that a good 308 would probably outshoot, by a little, a good 30-06, however for 1000 yards, the 06 seemed to do better. Never owned a magnum, and I never felt the "need" to use one for target shooting. To each his own though.
These days, if you are looking at National Match course competition, I would thing that an AR15 type rifle, whatever name it's maker might stick on it, would be the way to go. Things have changed. As foir used rifles, who knows, you might get a good one, but then you might be better off starting off with something new. Shop around. Good luck.