My experience: the smaller 20 mm objectives (I used a 1.5-5x Vari-X lll for awhile) are noticeably darker in the shadows and at either end of the day-too much so for my tastes.
I used a 1.75-6x Leupold in Namibia and found the power range ideal for me but even better in the grey-brown bush was the heavy duplex in it. I've also used the German 4a and liked it in those situations as well.
A lot of scopes will work but IMO stay away from a fine reticle for use on a big black animal that will probably be in the bush.
