Not sure if they achieved it mate but back home had a B763 pilot tell me he could give me 360KIAS on the drop.
447 KIAS seems quite impressive:
This had peaked at 20,000 ft/min with the aircraft pitched 30° nose-down after the aircraft had been rolled to the left. The control forces remained high but the commander considered this to be due to the aircraft’s speed, which he observed at a maximum of 447 kt.
http://www.aaib.gov.uk/cms_resources...JK%2009-10.pdf
I think the record is probably held by Hoot Gibson in the TWA 727 though:
TWA Flight 841 (1979) - Wikipedia, the free encyclopedia