Solo'd on THF75/NIN37... with capped marksmanship (230) and evasion at about 265.
I was in the middle of a coin trading run, so I did not have any food on me, unfortunately.
I made sure to keep him blind, with defense down, using bolts.
Echo Drops are pretty much a necessity, as he hits pretty hard (140-160) with low delay, making recovery from a long silence very tough.
Orobon is definitely not one of the toughest NM's that are soloable.
I believe one would be safe attempting to solo with THF, NIN, or RDM/NIN.