It's worth using the provided EPs to get a sense of which mags you prefer.
You can sort of extrapolate wider FoVs from there.
I've liked the following for an 8" dob/newt:
35 Panoptic
32 Agena Astro/UO SWA
30 Takahashi (not a widefield but superb contrast and faultless colour)
27 Panoptics
24 Panoptics
24 Takahashi (see above
)
20 Nagler
For some reason, I have never warmed to the longer Naglers in dobs. I don't know why - maybe I've never tried them with a coma corrector, but they always seem to have too much curvature and coma for me.
To my eye, the Panoptics have a noticably flatter field with sharper stars.
YMMV,
Peter