Unless you more often than not use your scope on a setting other than its higher power, you might as well start it at the highest power.
I think this is where the term "boresight" originally came from. It has proven to be quite accurate, actually in one instance getting me on faster that way than my buddy who was using a Leopold boresighter.
But if you want a boresighter like the ones you are already using, go for a Leupold. Also, they have these laser pointer sights that are the same size as the caliber of your rifle. You chamber the laser boresighter which projects a dot on your target downrange, showing where the bullet will hit. Then you center your crosshairs on the projected dot. Have never used one, but in theory it should work really well, and quickly. Kind of pricey, though, compared to just looking in the chamber and through the barrel.
Jake