The only difference in the two from the info i can see would be the positive offset on one wheel and the negative offset on another.
The positive offset will put your wheel closer to the vehicle, while the negative offset will put your wheel further out from the wheel well giving a wider stance.
As far as backspacing, here is a quick equation you can use...
Wheel width ÷ 2 + offset + ½” = Backspacing
So to answer your backspace question... the one with +7 offset will have 5.03" of backspace and the one with -6 will have 4.51" of backspace.
My opinion (for the better look) is to go with the -6 offset for better stance without the wheel sticking too far out to have to make major modifications (Body mount chop, etc.)