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Interesting question.
It seems to me you have most focal lengths covered, so then it becomes a question of whether you should replace one you already own, and if so, which one. (I have the S5000 20mm BTW, which I actually quite like.)
I note that you have a very nice GOTO scope, so I assume you don't really need the wide field to help acquire an object in the FOV (such as can be an issue with shorter focal length EPs in an undriven dob). So then it seems to come down aesthetics. Which EP do you have that makes you feel most claustrophobic? Which focal length EP do you use the most?
In general, I suppose wide fields are for encompassing extended objects nicely framed in a surrounding context. (Who wants close ups of globulars if you can't see the overall shape and contrast?) Probably that means you would want a longer focal length widefield. (What is the focal length of a 200R, anyway?) Maybe someone would say you should go the greNagler (31mm).
Type 4 naglers have longer eye relief that type 6, I think, and more black beaning. Type 6s are sharper across the field, I think. Complicated EPs with lots more glass will make for dimmer images. In the shorter focal lengths I would consider the Pentax XWs.
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