kobear, I agree with NYbowhunter if you only will take this shot on an animal of a certain status to be mounted or considered a trophy confuses me as well. Not only should any shot you take exude confidence of a clean harvets, it is the absolute worst shot to take for a shoulder mount, as it will make a mess of the cape.

To the orginal question, I don't take head on shot due to many reasons, but I will sum it up as they can only be considered marginal at best. Why I say this is too many horror stories both heard and seen to even consider it!! The quarter to depends on "how much" a quarter, but I have taken a good number of animals with quartering shots all resulting in clean kills. I prefer and have taken more with the slight quarter away shot angle though. Plain and simple the only guy that can determine if the shot presented is acceptable to a good result/outcome is the guy behund the crosshairs and trigger. If your not comfortable best wait and possibly not shoot. 3-P's are very important with hunting and shooting.
Practice
Patience
Persistance