For such a long run, you might consider an inline fan (google fantech
inline fan) As a bonus, they are much quieter than even the best
ceiling mount fans. (but more $$ too).

I've got one and they're great, well worth the added cost. I put one of
their low-voltage light/intake assemblies in the tub/shower ceiling. An
informal test using some strips of plastic showed no significant change in
intake power between the fan ducted into just the attic space (during
construction) and then using insulated ducting to a side vent on the gable
about 16' away. But a roof vent will certainly give better flow and will
probably cost a lot less than running extra insulated ducting.