I actually believe that the 8x57 could produce a slight advantage over the .270 win., because it can deliver a heavier bullet at velocities slightly greater than that from a .270 shooting a significantly lighter projectile. I think this would likely produce better penetration.
This is a common misconception. If you have bullets of equal, or near equal weights fired from different caliber guns the larger caliber gun will generally shoot them faster. You can shoot heavier bullets in larger caliber guns at about the same speeds as lighter bullets from smaller caliber guns. This is all true
150 years ago when projectiles were simple lead balls or cones this was important to ensure penetration in game. With simple lead projectiles heavier always out penetrated lighter. But with modern bullets not so. Bullet weight is still a factor, but construction is far more important today. Weight is only a factor in that within the same caliber, heavier bullets are longer bullets.
A 270, 30-06, and 8X57 will all shoot 150 gr bullets at, or just under 3000 fps. But because the 270 bullet is the smaller diameter, and longer bullet it will always outpenetrate the other 2 if all are using 150 gr bullets. Because it is more aerodynamic, it will maintain that speed better and will be MUCH faster and shoot MUCH flatter as range increases. With larger diameter bullets you have to move up significantly in weight to get equal penetration. The trade off with heavier, slower bullets is a more arched trajectory.
Generally speaking longer bullets penetrate better. A 270/150 gr, a 30-06/180gr, and an 8mm/200 gr are going to all penetrate about equal amounts when they hit game. It would be about a wash with all 3 assuming you were using the same bullet in all 3. Start shooting a Partition or TTSX in one and a Hornady SST in the others and then it becomes a matter of which is using the better bullet, not the caliber, speed or bullet weight.