Re: Will I be able to reach out to 500 yards?
If your question is weather the balistics calculator is a reliable way to shoot 500 yrds at an elk, I would ask what choice do you have? I have never used this elk hunting, but have used a range finder the last few years. Most cases elk don't give much time to 'calculate'. I have been used to the practice and guess plan, if you have time to use your balistics calculator by all means do it. I have been witness to many newcomers to my area who guess yardage way short or think they can shoot long range. Both groups either blast away never coming close and scare all the elk into the next county or wound 2 or 3 elk to take home one.
I cannot tell you what is ethical cause only you know your abilities. Practice much, err on the side of ethical and don't let elk fever get the better of you. That's the best advice I can give. As far as the caliber you don't have anything to worry about as far as knock down. Its all in delivering where it counts.
Hope this helps, good luck.