First I respect your concern for a humane kill.
I wouldn't worry about more power than what you've got; you were on the right track when you said you'd practice more from a wider variety of field positions. That's the key; a poorly placed shot from a 300 Mag (for example) won't do any better for you than one from your 280 AI. A well placed shot from your 280 AI is certain to do better than a poorly placed one from the 300 Mag.
Also don't believe the DRT hype. Everyone should strive for humane kills but expect anomalies along the way.
Practice hard and know your limits; maintain respect for your query and you're doing your part.
Nice write up keep up the good work!
