Sounds like you have never shot at those distances before. I think your equipment is up to the task. Last year I used a Leupold MK 4 3-9 MRT and wouldn't have have hesitated to take a shot at that range, and my targets were quite a bit smaller then an elk. I have never hunted elk but have seen them and they are pretty darn big. Find something the size of an elk, maybe a horse, and set up 700 yards out and look at it through your scope. If you don't think you have enough power then you should change out your scope, but it just sounds to me like you need to go out and shoot....A LOT!
Courage is just fear that has said it's prayers.
The people trying to say the 2nd Amendment is outdated are probably the same folks that would say the same thing about the Bible.