I snapped one for you. The nut is 1.75" on this one... for reference.
It's all subjective... but I tend to favor the nickel rounds. A little less ziiiing, and easier on the frets.
If it helps (and at the advice of another member here), I started building up my own sets using bass and guitar strings. I like D'Addarios, and so on my Hamer B8S I'm currently using a set of EXL220Ms for the roots (95s, but with a .045 G from an EXL170 set), and the bottom four strings from a pack of EXL110BT balanced tension 10s for the octaves. Working out pretty good so far. If I restring my B12s, I'll probably do the same thing - just adding a second octave of the same gauge.
Not sure if/how the guitar strings would fit a long scale, though. Gotta redo my 4003s/8 at some point, and so I'll find out soon enough.