I would never buy a scope by caliber. I base my scope purchases on usage.
Called predators under 300 yards a lower powered scope with a lot of FOV is my choice, you can pretty much hold on fur for every shot so things like turrets and busy reticles aren't necessary. More FOV will give you faster target acquisition and ability to track a moving critter through the brush and trees. For this kink of work I like to see a scope with at least 40' of FOV on the bottom end and I always keep my scopes on the bottom number while hunting. I've found that if you need more X's for the shot there is usually time to turn the scope up, when you need the large FOV there is no time to turn it down. I find 1-4 and 1.5-6 scopes work well for me, 2-7 and 2/2.5-10 scopes fit in here also. I feel very claustrophobic with 3x on the bottom end.
For open country where a number of shots are going to be over 300 yards, ballistic reticles and turrets come into play. Again I like a lot of FOV on the bottom, how many times has one shown up from the wrong direction at 20 yards and your looking out across the prairie for one. Here is where a 2/2.5-10 scope comes in handy kept on the bottom setting until you need the extra X's. Here one of the 3-15 scopes shine.
Good luck in your choices.
I don't think I can remember ever being under scoped but I know I've been over scoped more than once.
