with the right bullets and loads, they are both just as good.
I have never done 600 yard shooting, I, mostly do, 100 / 200 / and 300 yardage. So far, my accuracy is best with my 30-06, much much much better than my 300 win mag. Why ? because I practice the '06 alot more than I do my 300 so Im more familure with the gun and the caliber. My best days with my winchester model-70 '06 are just a shade under 1" @ 300 yards. With the 300 win mag, I am not even touching 1.5" and THATS my best days.
As far as bullet selection goes, I love the 180 gr Accubonds for the '06 (300 yard only) or the 180 gr remin core lokts (100 and 200 yards).
Now here is an idea that I have never tried yet, some people will disagree with me on this one, but I truely feel that my 7mm mag (winchester mod 70 XTR sporter 24" barrel) recoils a bit less than my synthetic winchester 70 30-06.... Dunno why.
However, you can do this 600 yard project of yours with a 7mm mag, shoots a tad bit flatter than a 06 and recoils about as much (if not less).