Most of these good programs will give you great data. If you make your 2 drop charts for sea level and for 6000 feet you should be fine out to the 600 to 700 yard ranges.
My recommendation for you is to be an Ethical hunter/shooter and check your zero after traveling like everyone should anyway. When you reach your elevation or hunting destination... shoot the rifle. If your new zero is a couple clicks lower, it will take care of your chart and you now have the confidence in it. Just mark on chart to know that the sea level and 6000 foot altitude is say 2 clicks or .5 MOA difference.
here is a great article for you to read....
Barometric Pressure and Ballistic Software