Both rounds are proven, as to bullets and straight line penetration, I always felt a high SD bullet like a heavier 6.5 would do better ALL ELSE Equal, as in Bullet Construction, less frontal area would not hamper penetration btw.
http://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/1483776/1http://www.24hourcampfire.com/ubbthreads..._test_Part_Deux6.5x47 have killed Elk to just under 1,000 yds...believe it was a 127 LRX.
As to either, on deer...hell I have killed enough in 6mmBR and 243 to choose Either, with a 95 ballistic tip out to easily 400 yds, and I will gladly shoulder punch them, did a double shoulder using a 243 on a 100 yd shot on a nice buck...sailed thru....
Deer I've shot are not wearing Kevlar...
Not doubting what happened, but it was likely Very bullet specific outlier, and shot angle. FWIW, I rarely shoot shoulders, but did above and proved the 95 BT did just like a 130 AB in a 260, same distance and size deer, both broadside.
I've got a 20" 308. I like my 6.5 CM much better. 
