It sounds like you are taking things to two extremes. To me a 4-12 scope is a varmint scope. A red dot is more for a defensive carbine like an AR. Quick and handy but not ideal for precision at long range.
I don't know why people put so much magnification on big game scopes. A 2-7 or 3-9 scope is all you'll ever need. Given the choice I would stick with the Leupold and leave it set on 4.
I personally think a red dot is a terrible choice for a 7mm Mag. A quality red dot is very expensive. You can buy yourself a very nice scope in the 2-7 or 3-9 range.