Yep, that's the tricky bit. I decided that Outstanding and Excellent are similar enough to treat as equivalents to be able to add a half-dozen or so threads that differed only in that one respect, but with greater differences the options bias the results differently and you can't really compare them well anymore.
For example in the format under consideration
I feel that "Good" and "So-So" tier differently than "Above Average" and "Average" (because I think the average Star Trek
novel is pretty good) and "Boring" is much more specific than "Below Average". I could see myself voting differently with those options than with the other options.
But it doesn't need to rely on just my judgement of course. If ever a consensus emerges that a particular poll format should be added (or for selection to work differently in general) for consideration I'm open to doing that.