i'm afraid i have to praise the 60Cx. use it for 15 months on the road now, and every day (when on the bike). The only thing is that due to vibrations the internal contacts from battery holder to circuit board got loose one time, after 40000km easy to fix yourself.
i have to say that the number of problems with the zumo series i witnessed in the dutch GS community are uncountable.
and they are fairly cheap these days, 60Cx even cheaper than 60Csx. the fairly long AA battery life, way more options for riding statistics etc.
if you want to be safe/sure consider the option to take a smaller and cheaper routing capable unit as backup like the eTrex HCx.
As for the Quest, personally i think the Quest is way to flimsy build (antenna mainly) for serious traveling, and very limited memory for map uploads, no memorycard options too, if i recall correct.