Re: 7mm Dakota
I think Lens' answer was spot on. Since (i'm guessing here) you'll be reloading, you can get the most from each chambering. All can be down-loaded a bit, but you may find the 7mm REM to be accomplish most of what the others can do in a more efficient package.
"I have a very strict gun control policy: if there’s a gun around, I want to be in control of it.”
— Clint Eastwood