good on yer!
never managed a 100k patrol, came real close only once (but that was in stock sh3)
had something similar last night, also a wolfpacked convoy, but only one black swan left, easy pickings
also torpedoed some large cargos, they only had the one tanker (sunk that too), this time the large cargoes blew up from the first fish (must have been carrying ammo or something)
I usually find that large cargos only need one fish, strangely enough, they seem to get hit, think it over a bit, steam right on, zig zag for a while then suddenly plow right under after 10 to 20 minutes....strange
same goes for large merchants, they display similar behaviour when hit in the forward cargohold.