Speaking from experience, it is very frustrating to hit a boomer solidly and have it not detonate. Sometimes you can't even tell, but with a good scope you can see the hole.
The failures that I had were probably not velocity related. I hit a few targets that had a bad batch, or maybe got wet; wouldn't work for anyone. Once or twice, I had hits at the very top of a boomer. (If you can hit a boomer at that distance, surely you can hit the bottom half of a boomer, right?) Contents may settle during placement.
With 308, I was able to get detonations probably 3/4th up the hill. I did not manage to work my way up to the top, but at that range, 308 is practically an artillery shell anyway.
You have to be really, really good to get to the targets at the top of the hill if you start at the bottom. You see, the really good folks tend to start at the top...